ctdb/docs: Include ceph rados namespace support in man page

ctdb/docs: Include ceph rados namespace support in man page

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15665

Document the new optional argument to specify the namespace to be
associated with RADOS objects in a pool.

Pair-Programmed-With: Anoop C S <anoopcs@samba.org>
Signed-off-by: Günther Deschner <gd@samba.org>
Reviewed-by: Günther Deschner <gd@samba.org>
Reviewed-by: David Disseldorp <ddiss@samba.org>
Autobuild-User(master): Anoop C S <anoopcs@samba.org>
Autobuild-Date(master): Fri Jun 14 07:42:25 UTC 2024 on atb-devel-224

(cherry picked from commit 35f6c3f3d4a5521e6576fcc0dd7dd3bbcea041b2)