mgr: relax osd ok-to-stop condition on degraded pgs

mgr: relax osd ok-to-stop condition on degraded pgs

Right now, the "ok-to-stop" condition is relatively rigorous, it allows
stopping an osd only if no PG on it is non-active or degraded. But there
are situations in which an OSD is part of a degraded pg and the pg still
still have > min_size complete replicas after the OSD is stopped.

In 9750061d5d4236aaba156d60790e0b8bcd7cfb64, we changed from considering
just acting to using avail_no_missing (OSDs that have no missing objects).
When the projected pg_acting is constructed this way, we can safely compare
to min_size... even for a PG marked degraded.

Fixes: https://tracker.ceph.com/issues/49392
Signed-off-by: Xuehan Xu <xxhdx1985126@gmail.com>