mgr/cephadm: try to get FQDN for inventory address

mgr/cephadm: try to get FQDN for inventory address

Fixes: https://tracker.ceph.com/issues/54502
Signed-off-by: Tatjana Dehler <tdehler@suse.com>
(cherry picked from commit 4f14993b1667fff309cd9cd6f9dad638a5a7e502)

Conflicts:
	src/pybind/mgr/cephadm/services/cephadmservice.py
Fixed conflict because `get_keyring_with_caps` has not been
backported to octopus: https://github.com/ceph/ceph/pull/39677
	src/pybind/mgr/cephadm/services/monitoring.py
Fixed a few conflicts because the master contains some improvements
around handling URLs, e.g. https://github.com/ceph/ceph/pull/43579