Ability to watch referenced or managed Kubernetes resources

[turkenh]

Description of your changes

This PR introduces the capability of watching referenced or managed Kubernetes resources as an "alpha feature".

When provider started with --enable-watches argument, it will be possible to configure an Object to watch relevant resources by setting spec.watch: true which is off by default.

The implementation is heavily based on the realtime compositions in Crossplane (as suggested by @sttts), however, we still have a good amount of divergence due to the difference between use cases.

apiVersion: kubernetes.crossplane.io/v1alpha2
kind: Object
metadata:
  name: sample-object
spec:
  watch: true # Watch for changes to on the Configmap
  forProvider:
    manifest:
      apiVersion: v1
      kind: ConfigMap
      metadata:
        namespace: default
      data:
        sample-key: sample-value

Fixes #159
Fixes #212
Fixes #164
Fixes #138

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

1. Deploy provider kubernetes watches feature enabled with the help of the following:

apiVersion: pkg.crossplane.io/v1
kind: Provider
metadata:
  name: crossplane-contrib-provider-kubernetes
spec:
  package: "index.docker.io/turkenh/provider-kubernetes:v0.14.0-rc0.12.gc580206" # custom build from this PR
  runtimeConfigRef:
    name: provider-kubernetes
---
apiVersion: pkg.crossplane.io/v1beta1
kind: DeploymentRuntimeConfig
metadata:
  name: provider-kubernetes
spec:
  deploymentTemplate:
    spec:
      selector: {}
      strategy: {}
      template:
        spec:
          containers:
          - args:
            - --enable-watches
            name: package-runtime

2. Deploy the following Object which has a reference to a configmap and managing another configmap:

---
apiVersion: kubernetes.crossplane.io/v1alpha2
kind: Object
metadata:
  name: foo
spec:
  watch: true
  references:
  # Use patchesFrom to patch field from other k8s resource to this object
  - patchesFrom:
      apiVersion: v1
      kind: ConfigMap
      name: bar
      namespace: default
      fieldPath: data.sample-key
    toFieldPath: data.sample-key-from-bar
  forProvider:
    manifest:
      apiVersion: v1
      kind: ConfigMap
      metadata:
        namespace: default
      data:
        sample-key: sample-value
  providerConfigRef:
    name: kubernetes-provider
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: bar
  namespace: default
data:
  sample-key: sample-value

3. Touch (e.g. add a random label) referenced configmap (bar) and check for the log line with message "Enqueueing Object because referenced resource changed"

4. Touch (e.g. add a random label) managed configmap (foo) and check for the log line with message "Enqueueing Object because referenced resource changed"

[turkenh]

From e2e test logs:

    logger.go:42: 15:29:35 | case/0-apply | running command: [/home/runner/work/provider-kubernetes/provider-kubernetes/examples/object/testhooks/validate-watching.sh]
    logger.go:42: 15:29:38 | case/0-apply | Enabling watch feature for the provider
    logger.go:42: 15:29:39 | case/0-apply | deploymentruntimeconfig.pkg.crossplane.io/runtimeconfig-provider-kubernetes patched
    logger.go:42: 15:29:42 | case/0-apply | Patching referenced secret
    logger.go:42: 15:29:42 | case/0-apply | secret/bar patched
    logger.go:42: 15:29:45 | case/0-apply | Checking if the managed secret has been updated
    logger.go:42: 15:29:45 | case/0-apply | Checking if the managed secret has been updated...Success
    logger.go:42: 15:29:45 | case/0-apply | Patching managed secret
    logger.go:42: 15:29:45 | case/0-apply | secret/foo patched
    logger.go:42: 15:29:48 | case/0-apply | Checking if the object grabbed the new value at status.atProvider
    logger.go:42: 15:29:48 | case/0-apply | Checking if the object grabbed the new value at status.atProvider...Success
    logger.go:42: 15:29:48 | case/0-apply | Successfully validated the watch feature!
    logger.go:42: 15:29:48 | case/0-apply | Disabling watch feature for the provider

[sttts]

Looks a little distorted:

// Copyright 2024 The Crossplane Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

[sttts]

Oh, we really have that format in Crossplane?

[sttts]

Lgtm