Issue: Broken config when using commonLabels

[xunholy]

https://github.com/jetstack/google-cas-issuer/blob/59fa9efe63bf6d26ea7a833e4694c66045883017/deploy/charts/google-cas-issuer/templates/deployment.yaml#L16C7-L16C65

We use commonLabels to add consistent labels across all resources, in our case we're also using apps: for our own convention however, this line breaks because it adds it with the bespoke chartname.

This would be great if it could use the helper function and also ensure that all keypairs are unique otherwise we get the following errors:

Error: map[string]interface {}(nil): yaml: unmarshal errors:
  line 35: mapping key "app" already defined at line 29