Federation Sender & Appservice Pusher Stream Optimisations (#13251)

* Replace `get_new_events_for_appservice` with `get_all_new_events_stream`

The functions were near identical and this brings the AS worker closer
to the way federation senders work which can allow for multiple workers
to handle AS traffic.

* Pull received TS alongside events when processing the stream

This avoids an extra query -per event- when both federation sender
and appservice pusher process events.

synapse/storage/databases/main/events_worker.py

@@ -292,25 +292,6 @@ class EventsWorkerStore(SQLBaseStore):
 
         super().process_replication_rows(stream_name, instance_name, token, rows)
 
-    async def get_received_ts(self, event_id: str) -> Optional[int]:
-        """Get received_ts (when it was persisted) for the event.
-
-        Raises an exception for unknown events.
-
-        Args:
-            event_id: The event ID to query.
-
-        Returns:
-            Timestamp in milliseconds, or None for events that were persisted
-            before received_ts was implemented.
-        """
-        return await self.db_pool.simple_select_one_onecol(
-            table="events",
-            keyvalues={"event_id": event_id},
-            retcol="received_ts",
-            desc="get_received_ts",
-        )
-
     async def have_censored_event(self, event_id: str) -> bool:
         """Check if an event has been censored, i.e. if the content of the event has been erased
         from the database due to a redaction.