Merge pull request #59417 from nbalacha/wip-nbalacha-ns-mirroring

rbd-mirror: allow mirroring to a different namespace

Reviewed-by: Ilya Dryomov <idryomov@gmail.com>

diff --cc src/cls/rbd/cls_rbd_client.cc
Simple merge

diff --cc src/cls/rbd/cls_rbd_client.h
Simple merge

diff --cc src/librbd/librbd.cc
Simple merge

diff --cc src/test/cli/rbd/help.t
Simple merge