What this PR does / why we need it:

This is a rework of an earlier merge request #443 to add an initial rollout size within HelmChartProxy.

This change adds in a new optional field called rollout, using which you can define an initial step size, optionally an increment size and a limit to how much the rollout step size can be increased to. These options can be defined individually for installs vs upgrade operations, allowing you to setup a different strategy for each kind of operation. Rollout quantities can be defined as an integer or a percentage of the total matched count of clusters. Below is an example showing the rollout option:

apiVersion: addons.cluster.x-k8s.io/v1alpha1
kind: HelmChartProxy
metadata:
  name: metallb
spec:
  rollout:
    install:
      stepInit: 10%
      stepIncrement: 5%
      stepLimit: 25%
    upgrade:
      stepInit: 10%
      stepIncrement: 5%
      stepLimit: 25%
  clusterSelector:
    matchLabels:
      MetalLBChart: enabled
  repoURL: https://metallb.github.io/metallb
  chartName: metallb
  releaseName: metallb

A new status condition HelmReleaseProxiesRolloutCompleted is added to denote rollout progress and is baked into the overall Ready condition set at the resource level.