feat(argo-rollouts): Add hpa to handle controller scaling

[vitorscassiano]

Add support to turn-on HPA on argo rollouts controller.

Checklist:

• I have bumped the chart version according to versioning
• I have updated the documentation according to documentation
• I have updated the chart changelog with all the changes that come with this pull request according to changelog.
• Any new values are backwards compatible and/or have sensible default.
• I have signed off all my commits as required by DCO.
• My build is green (troubleshooting builds).

[yu-croco]

*sorry, it's still draft PR. 🙈

[dihteixeira]

@vitorscassiano According to semantic versioning, the next version after 2.35.2 would be 2.35.3. Following the convention, the last part of the version (in this case, the "2") would be incremented to indicate a fix or patch, while keeping the previous parts unchanged.

[vitorscassiano]

I followed the versioning guide described in this document link. If I understand correctly, these changes include new functionality for the controller, so we should update the minor version, right?

[dihteixeira]

The HorizontalPodAutoscaler (HPA) template looks well-structured and follows the conventions commonly seen in Kubernetes YAML manifests. However, I can provide some suggestions for improvement:
Consistency in Label Indentation: Ensure consistency in label indentation. Currently, you're using nindent 4 for some labels and not for others. It's better to maintain consistency for readability.
Conditional Checks: It's good that you have conditional checks using if statements to enable or disable autoscaling based on configuration. This provides flexibility.
Validation of Configurations: Verify that the values provided for minReplicas and maxReplicas are within acceptable ranges and that the autoscaling metrics and behaviors are configured correctly for your application's requirements.

Overall, your template seems well-structured and should work effectively for configuring HorizontalPodAutoscaler in Kubernetes environment

[vitorscassiano]

The generated yaml are well-structured:

# Source: argo-rollouts/templates/controller/hpa.yaml
apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: release-name-argo-rollouts
  namespace: "moonlight-pipeline"
  labels:
    app.kubernetes.io/component: rollouts-controller
    helm.sh/chart: argo-rollouts-2.36.0
    app.kubernetes.io/name: argo-rollouts
    app.kubernetes.io/instance: release-name
    app.kubernetes.io/version: "v1.6.6"
    app.kubernetes.io/managed-by: Helm
    app.kubernetes.io/part-of: argo-rollouts
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: release-name-argo-rollouts
  minReplicas: 2
  maxReplicas: 4
  metrics:
    - type: Resource
      resource:
        name: memory
        target:
          type: Utilization
          averageUtilization: 80
    - type: Resource
      resource:
        name: cpu
        target:
          type: Utilization
          averageUtilization: 80

[yu-croco]

Hi @vitorscassiano , thank you for your PR.
Can you please create values.yaml for testing autoscaling, like below? 🙋
Ref: https://github.com/argoproj/argo-helm/blob/main/charts/argo-cd/ci/ha-autoscaling-values.yaml#L8-L16