cephadm: Add pre_remove and ensure deployment values are reset and API settings are updated when removing Prometheus or Alertmanager daemons
This fixes an issue where the dashboard API settings are not updated
properly when the active Prometheus or Alertmanager daemon is removed.
If the active daemon is removed, the settings are reconfigured to point
to a remaining daemon or reset if no daemons are available.
This avoids dashboard errors like "404 Not Found" caused by stale API
host settings.