feat: impersonated ack event

the matrix client-server spec actually doesn't say anything about
passing user_id as param:
https://spec.matrix.org/latest/client-server-api/#post_matrixclientv3roomsroomidreceiptreceipttypeeventid
however matrix-bot-sdk inside its "doRequest" method adds it as query
parameter nonetheless:
4fb43f174e/src/MatrixClient.ts (L2005)
4fb43f174e/src/MatrixClient.ts (L1201)
maybe it just works on some servers?

src/aioappsrv/app.py

@@ -226,11 +226,12 @@ class AppService:
 			self.logger.debug("sent message %s to %s as %s : %s", text, room, mxid, doc)
 			return doc["event_id"]
 
-	async def ack_event(self, room: str, event: str) -> None:
+	async def ack_event(self, room: str, event: str, mxid:  str | None = None) -> None:
 		async with self._client.request(
 			method="POST",
 			url=f"{self.client_api}/rooms/{room}/receipt/m.read/{event}",
 			headers=self.api_headers,
+			params={"user_id": mxid} if mxid else {},
 		) as res:
 			res.raise_for_status()