✨(backend) add roomkit viewset to start a room without WebRTC join

Introduce a new viewset that lets the roomkit start a room even when
no WebRTC participant has joined yet.

This is a first entry point that will be extended over time with
more actions a roomkit needs to be able to trigger.

Known limitations:

* The responsibility around SIP rules is currently split between
  the telephony feature and the roomkit one. This may need a
  refactor later on to consolidate ownership in a single place.
* The default throttle might be too low for production usage and
  will likely need to be revisited.

src/backend/core/services/livekit_events.py

@@ -245,7 +245,7 @@ class LiveKitEventsService:
         except models.Room.DoesNotExist as err:
             raise ActionFailedError(f"Room with ID {room_id} does not exist") from err
 
-        if settings.ROOM_TELEPHONY_ENABLED:
+        if settings.ROOM_TELEPHONY_ENABLED or settings.ROOMKIT_ENABLED:
             try:
                 self.telephony_service.create_dispatch_rule(room)
             except TelephonyException as e:
@@ -265,7 +265,7 @@ class LiveKitEventsService:
             )
             raise ActionFailedError("Failed to process room finished event") from e
 
-        if settings.ROOM_TELEPHONY_ENABLED:
+        if settings.ROOM_TELEPHONY_ENABLED or settings.ROOMKIT_ENABLED:
             try:
                 self.telephony_service.delete_dispatch_rule(room_id)
             except TelephonyException as e: