expose the default value for replace_existing

[NerdyShawn]

It wasn't apparent to me that the replace_existing parameter was available until I reviewed the documentation. This is mostly because I converted the helm chart to be a flux helmRelease which doesn't translate the comments to the artifact for flux's helm-controller. My thought was rather than uncomment the lines in the value just show it with its default of false and that way users can just change the value in the chart to override.

For example with flux creation

flux create hr cluster-secret --target-namespace=clustersecret --source=HelmRepository/cluster-secret --chart=cluster-secret --values=./values.yaml --export > helmrelease-cluster-secret.yaml

viewing the artifiact below that the helm-controller will use you can see that its not immediately apparent that replace_existing value is even used.

cat helmrelease-cluster-secret.yaml 
---
apiVersion: helm.toolkit.fluxcd.io/v2
kind: HelmRelease
metadata:
  name: cluster-secret
  namespace: flux-system
spec:
  chart:
    spec:
      chart: cluster-secret
      reconcileStrategy: ChartVersion
      sourceRef:
        kind: HelmRepository
        name: cluster-secret
  interval: 1m0s
  targetNamespace: clustersecret
  values:
    affinity: {}
    image:
      repository: quay.io/clustersecret/clustersecret
      tag: 0.0.11
    imagePullSecrets: []
    kubernetesClusterDomain: cluster.local
    nodeSelector: {}
    podAnnotations: {}
    tolerations: []