osd/OSDCap: allow rbd.metadata_list method under rbd-read-only profile

osd/OSDCap: allow rbd.metadata_list method under rbd-read-only profile

This was missed in commit acc447d5de7b ("osd/OSDCap: rbd profile
permits use of rbd.metadata_list cls method") which adjusted only
"profile rbd" OSD cap.  Listing image metadata is an essential part
of opening the image and "profile rbd-read-only" OSD cap must allow
it too.

While at it, constrain the existing grant for rbd profile from "any
object in the pool" to just "rbd_info object in the global namespace of
the pool" as this is where pool-level image metadata actually lives.

Fixes: https://tracker.ceph.com/issues/61382
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>