doc: updated Ceph documentation links
Fixes include:
- Updating Doxygen link for reference (http://docs.ceph.com/docs/master/dev/documenting/)
- Adding :ref: label for User Management page (http://docs.ceph.com/docs/master/rados/operations/user-management/)
- Update User Management link for reference (http://docs.ceph.com/docs/master/rbd/rbd-snapshot/)
Fixes: https://tracker.ceph.com/issues/37793
Signed-off-by: James McClune <jmcclune@mcclunetechnologies.net>
(cherry picked from commit
7ff2f215a3d051c4ef226bfdc81184d89520e152)