[STAN] Add subscriptions data stream metric types

[gpop63]

What does this PR do?

Add metric types for subscriptions data stream fields.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Relates STAN TSDB Enablement #7859

Screenshots

The dashboard for STAN metrics seems to be broken (this has to be addressed). I recreated the lenses just for visualization and data validation.

[elasticmachine]

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Build stats

• Start Time: 2023-10-30T10:14:47.543+0000

• Duration: 19 min 58 sec

Test stats 🧪

Test	Results
Failed	0
Passed	17
Skipped	0
Total	17

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[gpop63]

Rollover test

{
  "acknowledged": true,
  "shards_acknowledged": true,
  "old_index": ".ds-metrics-stan.subscriptions-default-2023.09.21-000001",
  "new_index": ".ds-metrics-stan.subscriptions-default-2023.09.21-000002",
  "rolled_over": true,
  "dry_run": false,
  "conditions": {}
}

Mappings

        "stan": {
          "properties": {
            "cluster": {
              "properties": {
                "id": {
                  "type": "keyword",
                  "time_series_dimension": true
                }
              }
            },
            "server": {
              "properties": {
                "id": {
                  "type": "keyword",
                  "time_series_dimension": true
                }
              }
            },
            "subscriptions": {
              "properties": {
                "channel": {
                  "type": "keyword",
                  "time_series_dimension": true
                },
                "id": {
                  "type": "keyword",
                  "time_series_dimension": true
                },
                "last_sent": {
                  "type": "long",
                  "time_series_metric": "counter"
                },
                "offline": {
                  "type": "boolean"
                },
                "pending": {
                  "type": "long",
                  "time_series_metric": "gauge"
                },
                "queue": {
                  "type": "keyword",
                  "time_series_dimension": true
                },
                "stalled": {
                  "type": "boolean"
                }
              }
            }
          }
        }

[gpop63]

TSDB testing kit output:

Testing data stream metrics-stan.subscriptions-default.
Index being used for the documents is .ds-metrics-stan.subscriptions-default-2023.10.18-000001.
Index being used for the settings and mappings is .ds-metrics-stan.subscriptions-default-2023.10.18-000001.

The time series fields for the TSDB index are: 
        - dimension (14 fields):
                - agent.id
                - cloud.account.id
                - cloud.availability_zone
                - cloud.instance.id
                - cloud.provider
                - cloud.region
                - container.id
                - host.name
                - service.address
                - stan.cluster.id
                - stan.server.id
                - stan.subscriptions.channel
                - stan.subscriptions.id
                - stan.subscriptions.queue
        - counter (1 fields):
                - stan.subscriptions.last_sent
        - gauge (1 fields):
                - stan.subscriptions.pending
        - routing_path (14 fields):
                - agent.id
                - cloud.account.id
                - cloud.availability_zone
                - cloud.instance.id
                - cloud.provider
                - cloud.region
                - container.id
                - host.name
                - service.address
                - stan.cluster.id
                - stan.server.id
                - stan.subscriptions.channel
                - stan.subscriptions.id
                - stan.subscriptions.queue

Index tsdb-index-enabled successfully created.

Copying documents from .ds-metrics-stan.subscriptions-default-2023.10.18-000001 to tsdb-index-enabled...
All 14261 documents taken from index .ds-metrics-stan.subscriptions-default-2023.10.18-000001 were successfully placed to index tsdb-index-enabled.

[agithomas]

LGTM!

[elasticmachine]

Package stan - 1.4.1 containing this change is available at https://epr.elastic.co/search?package=stan