Expose src Dispatch for rare complex scenarios

RELEASE_NOTES.md

@@ -10,7 +10,7 @@
 
 ## New Features
 
-<!-- Here goes the main new features and examples or instructions on how to use them -->
+- `DispatchInfo._src` was added for rare complex scenarios where the source of a dispatch needs to be accessed.
 
 ## Bug Fixes
 

src/frequenz/dispatch/_actor_dispatcher.py

@@ -32,6 +32,9 @@ class DispatchInfo:
     options: dict[str, Any]
     """Additional options."""
 
+    _src: Dispatch
+    """The dispatch that triggered this update."""
+
 
 class ActorDispatcher(BackgroundService):
     """Helper class to manage actors based on dispatches.
@@ -224,11 +227,12 @@ def start(self) -> None:
         self._tasks.add(asyncio.create_task(self._run()))
 
     async def _start_actor(self, dispatch: Dispatch) -> None:
-        """Start all actors."""
+        """Start the actor the given dispatch refers to."""
         dispatch_update = DispatchInfo(
             components=dispatch.target,
             dry_run=dispatch.dry_run,
             options=dispatch.payload,
+            _src=dispatch,
         )
 
         identity = self._dispatch_identity(dispatch)