feat: hpa with cpu + mem util scaling options

[burnjake]

• [ ] CHANGELOG.md updated - n/a?
• [ ] Rebased/mergable
• [x] Tests pass (see comment below)
• [x] Sign CLA (if not already signed)

We would like to scale the number of replicas based on usage which is a slight pain currently as you have to set the deployment.spec.replicas field to none if we were to roll our own HPA resource. There's also a pre-existing issue: https://github.com/influxdata/helm-charts/issues/624.

$ helm version
version.BuildInfo{Version:"v3.14.2", GitCommit:"c309b6f0ff63856811846ce18f3bdc93d2b4d54b", GitTreeState:"clean", GoVersion:"go1.22.0"}

Setting autoscaling.enabled: true templates the following Deployment and HPA resources:

$ cat values.yaml | grep autoscaling -A10
autoscaling:
  enabled: true
  minReplicas: 1
  maxReplicas: 5
  targetCPUUtilizationPercentage: 80
  targetMemoryUtilizationPercentage: 80
  behavior: {}

$ helm template ./ -s templates/deployment.yaml
---
# Source: telegraf/templates/deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: release-name-telegraf
  labels:
    helm.sh/chart: telegraf-1.8.43
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/name: telegraf
    app.kubernetes.io/instance: release-name
spec:
  selector:
    matchLabels:
      app.kubernetes.io/name: telegraf
      app.kubernetes.io/instance: release-name
  template:
    metadata:
      labels:
        app.kubernetes.io/name: telegraf
        app.kubernetes.io/instance: release-name
      annotations:
        checksum/config: 11e7bc3db613c177911535018f65051a22f67ef0cf419dc2f19448d2a629282f
    spec:
      serviceAccountName: release-name-telegraf
      containers:
      - name: telegraf
        image: "docker.io/library/telegraf:1.29-alpine"
        imagePullPolicy: "IfNotPresent"
        resources:
          {}
        env:
        - name: HOSTNAME
          value: telegraf-polling-service
        volumeMounts:
        - name: config
          mountPath: /etc/telegraf
      volumes:
      - name: config
        configMap:
          name: release-name-telegraf

$ helm template ./ -s templates/horizontalpodautoscaler.yaml
---
# Source: telegraf/templates/horizontalpodautoscaler.yaml
apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: release-name-telegraf
  labels:
    helm.sh/chart: telegraf-1.8.43
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/name: telegraf
    app.kubernetes.io/instance: release-name
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: release-name-telegraf
  minReplicas: 1
  maxReplicas: 5
  metrics:
    - type: Resource
      resource:
        name: memory
        target:
          type: Utilization
          averageUtilization: 80
    - type: Resource
      resource:
        name: cpu
        target:
          type: Utilization
          averageUtilization: 80

Setting autoscaling.enabled: false templates the following Deployment resource:

$ cat values.yaml | grep autoscaling -A10
autoscaling:
  enabled: false
  minReplicas: 1
  maxReplicas: 5
  targetCPUUtilizationPercentage: 80
  targetMemoryUtilizationPercentage: 80
  behavior: {}

helm template ./ -s templates/deployment.yaml
---
# Source: telegraf/templates/deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: release-name-telegraf
  labels:
    helm.sh/chart: telegraf-1.8.43
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/name: telegraf
    app.kubernetes.io/instance: release-name
spec:
  replicas: 1
  selector:
    matchLabels:
      app.kubernetes.io/name: telegraf
      app.kubernetes.io/instance: release-name
  template:
    metadata:
      labels:
        app.kubernetes.io/name: telegraf
        app.kubernetes.io/instance: release-name
      annotations:
        checksum/config: 11e7bc3db613c177911535018f65051a22f67ef0cf419dc2f19448d2a629282f
    spec:
      serviceAccountName: release-name-telegraf
      containers:
      - name: telegraf
        image: "docker.io/library/telegraf:1.29-alpine"
        imagePullPolicy: "IfNotPresent"
        resources:
          {}
        env:
        - name: HOSTNAME
          value: telegraf-polling-service
        volumeMounts:
        - name: config
          mountPath: /etc/telegraf
      volumes:
      - name: config
        configMap:
          name: release-name-telegraf

$ helm template ./ -s templates/horizontalpodautoscaler.yaml
Error: could not find template templates/horizontalpodautoscaler.yaml in chart

An example with behaviour:

$ cat values.yaml | grep autoscaling -A20
autoscaling:
  enabled: true
  minReplicas: 1
  maxReplicas: 5
  targetCPUUtilizationPercentage: 80
  targetMemoryUtilizationPercentage: 80
  behavior:
    scaleDown:
      policies:
      - type: Pods
        value: 4
        periodSeconds: 60
      - type: Percent
        value: 10
        periodSeconds: 60

$ helm template ./ -s templates/horizontalpodautoscaler.yaml
---
# Source: telegraf/templates/horizontalpodautoscaler.yaml
apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: release-name-telegraf
  labels:
    helm.sh/chart: telegraf-1.8.43
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/name: telegraf
    app.kubernetes.io/instance: release-name
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: release-name-telegraf
  minReplicas: 1
  maxReplicas: 5
  behavior:
    scaleDown:
      policies:
      - periodSeconds: 60
        type: Pods
        value: 4
      - periodSeconds: 60
        type: Percent
        value: 10
  metrics:
    - type: Resource
      resource:
        name: memory
        target:
          type: Utilization
          averageUtilization: 80
    - type: Resource
      resource:
        name: cpu
        target:
          type: Utilization
          averageUtilization: 80