Add documentation for KEDA Webhook High Availability and topologySpreadConstraints

[pragmaticivan]

Currently, we have documentation for the operator and metrics API, but not for webhooks.

While we are at it, I suggest we also include topologySpreadConstraints examples for zones for all of them.

Ex:

operator:
  # While you can run more replicas of our operator, only one operator instance will be the leader and serving traffic.
  # You can run multiple replicas, but they will not improve the performance of KEDA, it could only reduce downtime during a failover.
  replicaCount: 3

metricsServer:
  # You can run multiple replicas of our metrics sever, and it is recommended to add
  # the --enable-aggregator-routing=true CLI flag to the kube-apiserver so that requests sent to our metrics servers are load balanced.
  # However, you can only run one active metric server in a Kubernetes cluster
  # serving external.metrics.k8s.io which has to be the KEDA metric server.
  replicaCount: 3

webhooks:
  replicaCount: 3

topologySpreadConstraints:
  operator:
  - labelSelector:
      matchLabels:
        app.kubernetes.io/name: keda-operator
        app.kubernetes.io/instance: keda
    maxSkew: 1
    topologyKey: topology.kubernetes.io/zone
    whenUnsatisfiable: DoNotSchedule
  metricsServer:
  - labelSelector:
      matchLabels:
        app.kubernetes.io/name: keda-operator-metrics-apiserver
        app.kubernetes.io/instance: keda
    maxSkew: 1
    topologyKey: topology.kubernetes.io/zone
    whenUnsatisfiable: DoNotSchedule
  webhooks:
  - labelSelector:
      matchLabels:
        app.kubernetes.io/name: keda-admission-webhooks
        app.kubernetes.io/instance: keda
    maxSkew: 1
    topologyKey: topology.kubernetes.io/zone
    whenUnsatisfiable: DoNotSchedule

podDisruptionBudget:
  operator:
    minAvailable: 1
  metricsServer:
    minAvailable: 1
  webhooks:
    minAvailable: 1

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you for your contributions.

[tomkerkhove]

Hey, are you willing to open a PR?