TLS support for clusters-service

[foot]

Fixes #532

• Modifies build process, now builds a gitops binary in a workflow if you need a ref other than main
  • Simon, 2022-03-11: This is locked to weaveworks/weave-gitops@931b52e (main) right now as a main has failed to build a new gitops binary due to more gitlab account locking.
• Removes the nginx-ingress-controller
  • Disables the alerting acceptance tests for now as they rely on the ingress-controller to talk to alertmanager
• clusters-service listens to TLS by default
• Helm chart updated w/ tls section where you can specify a TLS secret (e.g. as generated by cert-manager)

  tls:
    enabled: true
    # if no tls secret is specified then we generate it in-mem in the server
    secretName: ""
  

User-guide updates are in weaveworks/weave-gitops#1689

[yiannistri]

Looks great! 💯 💯 💯