Allow custom mount points to be added to vertica

[spilchen]

This adds the ability to add custom volume mounts to the Vertica container. A new spec.volumeMounts parameter was added to achieve this. It works alongside the spec.volumes parameter.

Here is an example that mounts the path /tenants in the Vertica container using an existing PVC.

apiVersion: vertica.com/v1beta1
kind: VerticaDB
metadata:
  name: verticadb-sample
spec:
  communal:
    ...
  subclusters:
  - name: sc1
  volumeMounts:
  - mountPath: /tenants
    name: tenants
  volumes:
  - name: tenants
    persistentVolumeClaim:
      claimName: vertica-pvc

The volumeMounts parameter takes the standard set of options for volume mounts (e.g. same as pod.spec.containers.volumeMounts).

The mount path for the new volume mount cannot conflict with any existing. The webhook was updated to detect any conflicts.

To avoid a circular dependency with the imports, I had to move a few helper functions in the paths package to api/v1beta1.