Log when stopping GrpcStreamBroadcaster instances

There's already a similar log message when starting to stream.

Signed-off-by: Sahas Subramanian <sahas.subramanian@proton.me>

Author: shsms

src/frequenz/client/base/streaming.py

@@ -88,6 +88,7 @@ def is_running(self) -> bool:
 
     async def stop(self) -> None:
         """Stop the streaming helper."""
+        _logger.info("%s: stopping the stream", self._stream_name)
         if self._task.done():
             return
         self._task.cancel()