mgr/dashboard: Allow the user to re-use existing r

mgr/dashboard: Allow the user to re-use existing r
ealm/zg/zone and setup replication

1. Currently, we just allow the user to create a new realm/zg/zone and setup replication using the multi-site replication wizard. The ask is to allow the user to select the pre-existing realm/zg/zone and setup replication via automatic export and import of token as well.

2. Enable rgw module automatically in the selected cluster if its not
   enabled

Fixes: https://tracker.ceph.com/issues/70276
Signed-off-by: Aashish Sharma <aasharma@redhat.com>