Changes to users / policies are not persisted properly if only one replica is used

[maltesander]

If NiFi is created with only one replica, and changes are made to users and/or polices (e.g. via UI), these changes are not persisted during pod restarts.
This is because we mount the config map containing the config files and copy them to an empty dir.
We should use a proper PVC for that case or document that cluster mode should require at least 2 replicas.

With more than 1 replica i could not reproduce it, i think the flow sync takes care of that properly.