ceph: send opened files/pinned caps/opened inodes metrics to MDS daemon

For the old ceph version, if it received this metric info, it will just
ignore them.

URL: https://tracker.ceph.com/issues/46866


Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>