feature: allow conditional creation of ServiceAccount

[wc-s]

So that the user can user their own ServiceAccount with such a values file:

serviceAccount:
  create: false
  name: my-sa

This allows the user to fine-tune the RBAC permissions, which is useful especially given the current default ClusterRole allows reading Secret objects.

[rocktavious]

@wc-s Thanks for the PR! You'll need to bump the chart version too so the auto release process doesn't fail. https://github.com/OpsLevel/helm-charts/blob/main/charts/kubernetes-sync/Chart.yaml#L4

[wc-s]

@rocktavious understood, thanks. Done.