[5/5] Document catalog zones member zone reset by change of unique label

The DNS catalog zones draft version 5 document requires that catalog zones consumers must reset the member zone's internal zone state when its unique label changes (either within the same catalog zone or during change of ownership performed using the "coo" property).

BIND already behaves like that, and, in fact, doesn't support keeping the zone state during change of ownership even if the unique label has been kept the same, because BIND always removes the member zone and adds it back during unique label renaming or change of ownership.

Document the described behavior and add a log message to inform when unique label renaming occurs.

Add a system test case with unique label renaming.

Closes #3225 (closed)