mgr/smb: prevent switching between clustering modes

mgr/smb: prevent switching between clustering modes

Prevent users from changing the cluster resource values such that a
cluster is changed from not using CTDB to using CTDB and vice versa.
This avoids complex situations that arise when making these sorts of
changes, in particular going from CTDB to non-CTDB which I am very sure
will mess up the tdb files.

Blocking these changes limits the need to test changing clustering
behavior on the fly. We can always revisit this in the future if needed.

Fixes: https://tracker.ceph.com/issues/68511
Signed-off-by: John Mulligan <jmulligan@redhat.com>