doc: Republishing the admin operations API for the gateway.

fixes: #4978

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
Merge branch 'master' of https://github.com/ceph/ceph
doc: Added the non-implemented bit for the gateway to the dev/radosgw TOC.

fixes: #4978

Signed-off-by: John Wilkins <john.wilkins@inktank.com>