Introduce datasources in package to configure inputs and streams

In elastic/beats#15940 datasources, inputs and streams are introduced into the agent config. To make it possible to configure these in the UI and through the API, some changes to the manifest definitions of a package and datasets are needed.

**Package manifest**

Each package must specify the datasources it supports with the supported inputs inside. So far all the packages only support one datasource but I want to keep the door open for this to potentially change in the future. It also makes it possible to have the manifest config of a datasource be identical to the config which ends up in the agent config.

The package manifest datasource definition looks as following (nginx example):

```
datasources:
  -
    # Do we need a name for the data source?
    name: nginx

    # List of inputs this datasource supports
    inputs:
      -
        # An id can be given, in case the type used here is not unique
        # This is for selection in the stream
        # id: nginx
        type: metrics/nginx

        # Common configuration options for this input
        vars:
          - name: hosts
            description: Nginx hosts
            default:
              ["http://127.0.0.1"]
            # All the config options that are required should be shown in the UI
            required: true
          - name: period
            description: "Collection period. Valid values: 10s, 5m, 2h"
            default: "10s"
          - name: username
            type: text
          - name: password
            # This is the html input type?
            type: password

      -
        type: logs

        # Common configuration options for this input
        vars:

      -
        type: syslog

        # Common configuration options for this input
        vars:

```

Inside the datasource, the supported inputs are specified with the common variables across all streams which use a certain input. In the UI I expect that we show the `required` configs by default and all the others are under "Advanced" or similar.

**Dataset manifest**

With the datasources and inputs defined on the package level, each dataset can specify which inputs it supports. Most datasets will only support one input for now. For the nginx metrics this looks as following:

```
inputs:
  - type: "metric/nginx"

    # Only the variables have to be repeated that are not specified as part of the input
    vars:
      # All variables are specified in the input already
```

As an example with supporting multiple inputs, we have the nginx error logs:

```
inputs:
  - type: log
    vars:
      - name: paths
        required: true
        default:
          - /var/log/nginx/error.log*
        os.darwin:
          - /usr/local/var/log/nginx/error.log*
        os.windows:
          - c:/programdata/nginx/logs/error.log*

  - type: syslog
    vars:
      # Are udp and tcp syslog input two different inputs?
      - name: protocol.udp.host
        required: true
        default:
          - "localhost:9000"
```

The log and syslog input are supported (not the case today, just an example). One the dataset level also all additional variables for this dataset are specified. The ones already specified on the input level in the package don't have to be specified again.

**Stream definition**

Now that the dataset has its supported inputs and variables defined, the stream can be defined. The stream defines which input it uses from the dataset and its configuration variables. Here an example for nginx metrics:

```
input: metrics/nginx
metricsets: ["stubstatus"]
period: {{period}}
enabled: true

hosts: {{hosts}}

{{#if username}}
username: "{{username}}"
{{/if}}
{{#if password}}
password: "{{password}}"
{{/if}}
```

During creation time of the stream config the variables from the datasource inputs and local variables from the dataset are filled in.

A stream definition could also support multiple inputs as seen in the following example:

```

{{#if input == log}}
input: log

{{#each paths}}
paths: "{{this}}"
{{/each}}
exclude_files: [".gz$"]

processors:
  - add_locale: ~
{{/if}}

{{#if input == syslog}}
input: syslog

{{/if}}
```

**Further changes**

* Rename `agent/input` to `agent/stream` as a stream is configured there.

dev/package-examples/nginx-1.2.0/dataset/error/agent/config/input.yml → dev/package-examples/nginx-1.2.0/dataset/access/agent/stream/stream.yml

@@ -1,8 +1,10 @@
-type: log
+
+input: log
+paths:
 {{#each paths}}
-paths: "{{this}}"
+  - "{{this}}"
 {{/each}}
-ingest_pipeline: {{pipeline}}
+
 exclude_files: [".gz$"]
 
 processors:

dev/package-examples/nginx-1.2.0/dataset/access/manifest.yml

@@ -8,18 +8,22 @@ type: logs
 # The ingest pipeline which should be used.
 ingest_pipeline: default
 
-vars:
-  - name: paths
-    # Should we define this as array? How will the UI best make sense of it?
-    type: textarea
-    default:
-      - /var/log/nginx/access.log*
-    # I suggest to use ECS fields for this config options here: https://github.com/elastic/ecs/blob/master/schemas/os.yml
-    # This would need to be based on a predefined definition on what can be filtered on
-    os.darwin:
-      - /usr/local/var/log/nginx/access.log*
-    os.windows:
-      - c:/programdata/nginx/logs/*access.log*
+# List of supported inputs
+inputs:
+  - type: log
+    vars:
+      - name: paths
+        required: true
+        # Should we define this as array? How will the UI best make sense of it?
+        type: textarea
+        default:
+          - /var/log/nginx/access.log*
+        # I suggest to use ECS fields for this config options here: https://github.com/elastic/ecs/blob/master/schemas/os.yml
+        # This would need to be based on a predefined definition on what can be filtered on
+        os.darwin:
+          - /usr/local/var/log/nginx/access.log*
+        os.windows:
+          - c:/programdata/nginx/logs/*access.log*
 
 requirements:
   elasticsearch.processors:

dev/package-examples/nginx-1.2.0/dataset/error/agent/stream/stream.yml

@@ -0,0 +1,23 @@
+
+# The selected input has to be passed to the stream config when processed.
+
+{{#if input == log}}
+input: log
+
+{{#each paths}}
+paths: "{{this}}"
+{{/each}}
+exclude_files: [".gz$"]
+
+processors:
+  - add_locale: ~
+{{/if}}
+
+
+# This is an example stream config on how multiple inputs could be supported
+
+{{#if input == syslog}}
+input: syslog
+
+# TODO: would need some more config options
+{{/if}}

dev/package-examples/nginx-1.2.0/dataset/error/manifest.yml

@@ -1,11 +1,27 @@
 title: Nginx Error Logs
 type: logs
 ingest_pipeline: pipeline
-vars:
-  - name: paths
-    default:
-      - /var/log/nginx/error.log*
-    os.darwin:
-      - /usr/local/var/log/nginx/error.log*
-    os.windows:
-      - c:/programdata/nginx/logs/error.log*
+
+
+# This is an example that multiple inputs are supported by one dataset
+inputs:
+  - type: log
+    vars:
+      - name: paths
+        required: true
+        default:
+          - /var/log/nginx/error.log*
+        os.darwin:
+          - /usr/local/var/log/nginx/error.log*
+        os.windows:
+          - c:/programdata/nginx/logs/error.log*
+
+  - type: syslog
+    vars:
+      # Are udp and tcp syslog input two different inputs?
+      - name: protocol.udp.host
+        required: true
+        default:
+          - "localhost:9000"
+
+

dev/package-examples/nginx-1.2.0/dataset/stubstatus/agent/input/input.yml → dev/package-examples/nginx-1.2.0/dataset/stubstatus/agent/stream/stream.yml

@@ -1,4 +1,4 @@
-type: metric/nginx
+input: metrics/nginx
 metricsets: ["stubstatus"]
 period: {{period}}
 enabled: true

dev/package-examples/nginx-1.2.0/dataset/stubstatus/manifest.yml

@@ -10,17 +10,10 @@ compatibility: linux, freebsd
 # Each input can be in its own release status
 release: beta
 
-vars:
-  - name: hosts
-    description: Nginx hosts
-    default:
-      ["http://127.0.0.1"]
-    required: true
-  - name: period
-    description: "Collection period. Valid values: 10s, 5m, 2h"
-    default: "10s"
-  - name: username
-    type: text
-  - name: password
-    # This is the html input type?
-    type: password
+# List of inputs this dataset supports
+inputs:
+  - type: "metric/nginx"
+
+    # Only the variables have to be repeated that are not specified as part of the input
+    vars:
+      # All variables are specified in the input already

dev/package-examples/nginx-1.2.0/manifest.yml

@@ -12,3 +12,45 @@ requirement:
     versions: ">7.1.0 <7.6.0"
   elasticsearch:
     versions: ">7.0.1"
+
+datasources:
+  -
+    # Do we need a name for the data source?
+    name: nginx
+
+    # List of inputs this datasource supports
+    inputs:
+      -
+        # An id can be given, in case the type used here is not unique
+        # This is for selection in the stream
+        # id: nginx
+        type: metrics/nginx
+
+        # Common configuration options for this input
+        vars:
+          - name: hosts
+            description: Nginx hosts
+            default:
+              ["http://127.0.0.1"]
+            # All the config options that are required should be shown in the UI
+            required: true
+          - name: period
+            description: "Collection period. Valid values: 10s, 5m, 2h"
+            default: "10s"
+          - name: username
+            type: text
+          - name: password
+            # This is the html input type?
+            type: password
+
+      -
+        type: logs
+
+        # Common configuration options for this input
+        vars:
+
+      -
+        type: syslog
+
+        # Common configuration options for this input
+        vars:

dev/package-examples/system-0.9.0/dataset/cpu/agent/stream/stream.yml

@@ -0,0 +1,6 @@
+input: metrics/system
+enabled: false # default true
+metricset: cpu
+period: 10s
+dataset: system.cpu
+metrics: ["percentages", "normalized_percentages"]

dev/package-examples/system-0.9.0/dataset/cpu/manifest.yml

@@ -5,4 +5,5 @@ release: beta
 # Needs to describe the type of this input
 type: metrics
 
-
+inputs:
+  - type: metrics/system

dev/package-examples/system-0.9.0/dataset/load/agent/stream/stream.yml

@@ -0,0 +1,4 @@
+inputy: metric/system
+enabled: true
+metricsets:
+  - load

dev/package-examples/system-0.9.0/dataset/load/manifest.yml

@@ -5,4 +5,5 @@ release: beta
 # Needs to describe the type of this input
 type: metrics
 
-
+inputs:
+  - type: system/metrics

dev/package-examples/system-0.9.0/dataset/memory/agent/stream.yml/stream.yml

@@ -0,0 +1,4 @@
+input: metric/system
+enabled: true
+metricsets:
+  - memory

dev/package-examples/system-0.9.0/dataset/memory/manifest.yml

@@ -5,4 +5,6 @@ release: beta
 # Needs to describe the type of this input
 type: metrics
 
+inputs:
+  - type: system/metrics
 

dev/package-examples/system-0.9.0/manifest.yml

@@ -10,3 +10,10 @@ release: ga
 requirement:
   kibana:
     versions: "<8.0.0"
+
+
+datasources:
+  - inputs:
+      type: metrics/system
+  - inputs:
+      type: log