mgr/cephadm: leverage service specs

mgr/cephadm: leverage service specs

Fixes: https://tracker.ceph.com/issues/44205
This does a couple of things:

* Change the way apply_$service() works:

Instead of triggering the deployment mechanism it will rather
transform the already passed ServiceSpec into a json representation
and save it in a persistent mon_store section.

`mgr/cephadm/service_spec/$service|daemon_type/service_name`

These locations will be periodically checked in the serve() thread.
This works since all the apply_$service_type functions are idempotent.

* Allow to save a config-like specification in the mon_store.

`ceph orch apply -i <service_spec_file.yaml>`

will read the specified services and save them in the mon store
section like mentioned above. The same serve() mechanism like above
also applies to deployment.

Signed-off-by: Joshua Schmid <jschmid@suse.de>