support timestamped appservice messaging

Co-authored-by: strawberry <strawberry@puppygock.gay>
Signed-off-by: strawberry <strawberry@puppygock.gay>

src/api/client/message.rs

@@ -84,6 +84,11 @@ pub(crate) async fn send_message_event_route(
 				unsigned: Some(unsigned),
 				state_key: None,
 				redacts: None,
+				timestamp: if body.appservice_info.is_some() {
+					body.timestamp
+				} else {
+					None
+				},
 			},
 			sender_user,
 			&body.room_id,