cooperative_replication works even if cluster parameter is not used

If cooperative_replication is enabled but the service does not use the cluster parameter, the behavior is to assume that the servers are owned. This is not ideal and the documentation is vague on the specifics of the behavior when cluster is not defined. To prevent multiple KafkaCDC instances from producing the same events, this should be treated as a configuration error.

However, since this is a significant change in behavior, this should not be done in a patch release.