[Autoscaling] Enable scale subresource on eligible resources

[barkbay]

This PR enables scale subresource on the following resources:

• ApmServer
• Kibana
• EnterpriseSearch
• ElasticMapsServer

If you want to give it a try:

• Update the CRDs with the ones provided by this PR
• Deploy the following resources:

apiVersion: elasticsearch.k8s.elastic.co/v1
kind: Elasticsearch
metadata:
  name: elasticsearch-sample
spec:
  version: 7.13.1
  nodeSets:
    - name: default
      count: 1
      config:
        node.store.allow_mmap: false
---
apiVersion: kibana.k8s.elastic.co/v1
kind: Kibana
metadata:
  name: kibana-sample
spec:
  version: 7.13.1
  count: 1
  elasticsearchRef:
    name: "elasticsearch-sample"
  podTemplate:
    spec:
      containers:
        - name: kibana
          resources:
            requests:
              memory: 1Gi
              cpu: 1
            limits:
              memory: 1Gi
---
apiVersion: autoscaling/v2beta2
kind: HorizontalPodAutoscaler
metadata:
  name: kb
spec:
  scaleTargetRef:
    apiVersion: kibana.k8s.elastic.co/v1
    kind: Kibana
    name: kibana-sample
  minReplicas: 1
  maxReplicas: 4
  metrics:
    - type: Resource
      resource:
        name: cpu
        target:
          type: Utilization
          averageUtilization: 50

• Stress the CPU by running the following command in the Kibana Pod: sha1sum /dev/zero

The deployment should scale up automatically after a few seconds.

Fix #4547

[barkbay]

jenkins test this please

[barkbay]

jenkins test this please

[pebrc]

LGTM! I did a simple test with Enterprise Search 👍

[pebrc]

One more thought: should we mention this new capability in the documentation?

[barkbay]

One more thought: should we mention this new capability in the documentation?

👍 , just opened #4608, I'll take care of it for 1.7.0