cephadm: fix osd adoption with custom cluster name

cephadm: fix osd adoption with custom cluster name

When adopting Ceph OSD containers from a Ceph cluster with a custom name, it fails
because the name isn't propagated in unit.run.
The idea here is to change the lvm metadata and enforce 'ceph.cluster_name=ceph'
given that cephadm doesn't support custom names anyway.

Fixes: https://tracker.ceph.com/issues/55654
Signed-off-by: Adam King <adking@redhat.com>
Co-authored-by: Guillaume Abrioux <gabrioux@redhat.com>