mgr/cephadm: show unmanaged OSDs under 'osd' service

mgr/cephadm: show unmanaged OSDs under 'osd' service

1- If the unit.meta file service_name = osd.NNN (which is true for lots of
OSDs deployed on older version of cephadm) then ignore the field entirely.

2- If an OSD has not service_name (see above) then show it under the 'osd'
service (instead of 'osd.unmanaged').

Sample 'ceph orch ls' output with a drivegroup + unmanaged OSD:

NAME      PORTS  RUNNING  REFRESHED  AGE  PLACEMENT
...
osd                    1  85s ago    -    <unmanaged>
osd.hdds               5  85s ago    2s   *
...

Fixes: https://tracker.ceph.com/issues/53235
Signed-off-by: Sage Weil <sage@newdream.net>