docs: rgw multisite docs with new rgw_instances config
docs: rgw multisite docs with new rgw_instances config

Docs reflect that each instance of `rgw_instances`
can now take rgw_zonemaster, rgw_zonesecondary,
rgw_zonegroupmaster, rgw_multisite_proto.

Signed-off-by: Ali Maredia <fe8379b4313c3a8f13a448418c8783dd04b778fa@redhat.com>

ceph/ceph-ansible,ceph/ceph-ansible