mgr/cephadm: using service registry pattern for cephadm services

mgr/cephadm: using service registry pattern for cephadm services

This change includes mainly the following enhancements:
- Introduced a centralized `CephadmServiceRegistry` to manage service registration and initialization.
- Added dynamic discovery of service modules in the same directory using `pkgutil` and `importlib`.
- Implemented a decorator `@service_registry_decorator` for automatic registration of service classes.

Fixes: https://tracker.ceph.com/issues/69021
Signed-off-by: Redouane Kachach <rkachach@ibm.com>