ReplicatedPG,rados: add CEPH_OSD_[COPY_FROM]_SNAPID_CLONE for promote

Otherwise, we don't have a way to distinguish between client requests where we
should return -ENOENT if the snapid is removed and promotion requests where we
should interpret the snapid as a clone id directly.

Fixes: #7858
Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG: improve get_object_context debugging

Signed-off-by: Samuel Just <sam.just@inktank.com>
Merge remote-tracking branches 'origin/wip-sam-testing2', 'upstream/wip-7659', 'origin/wip-7904', 'origin/wip-7858', 'origin/wip-7831' and 'origin/wip-7916' into wip-sam-testing