Improvement: Emit warning when using multiple RoleGroups without a myidOffset

[fhennig]

Context

The ZK operator uses the ordinal index of pods in the RoleGroup statefulsets to assign a myid to each replica. This approach leads to duplicate IDs when using more than one RoleGroup, als all indices are 0-based. To prevent ID collisions, a custom myidOffset needs to be specified, for which we wrote documentation.

Improvement

The operator doesn't do anything when there are multiple role-groups without an offset. The operator should at least emit a warning

Reference comment: #546 (comment)

[fhennig]

Maybe we could even make this an error? I think the operator shouldn't deploy Pods where it knows that ids will conflict. It's easy to track the IDs which are in use.

[lfrancke]

Agreed, this can be caught automatically I believe