Accept & store thread IDs for receipts (implement MSC3771). (#13782)

Updates the `/receipts` endpoint and receipt EDU handler to parse a
`thread_id` from the body and insert it in the database.

synapse/replication/tcp/client.py

@@ -427,7 +427,8 @@ class FederationSenderHandler:
                 receipt.receipt_type,
                 receipt.user_id,
                 [receipt.event_id],
-                receipt.data,
+                thread_id=receipt.thread_id,
+                data=receipt.data,
             )
             await self.federation_sender.send_read_receipt(receipt_info)
 

synapse/replication/tcp/streams/_base.py

@@ -361,6 +361,7 @@ class ReceiptsStream(Stream):
         receipt_type: str
         user_id: str
         event_id: str
+        thread_id: Optional[str]
         data: dict
 
     NAME = "receipts"