Support for MSC2285 (hidden read receipts) (#10413)

Implementation of matrix-org/matrix-doc#2285

synapse/replication/tcp/client.py

@@ -393,6 +393,11 @@ class FederationSenderHandler:
             # we only want to send on receipts for our own users
             if not self._is_mine_id(receipt.user_id):
                 continue
+            if (
+                receipt.data.get("hidden", False)
+                and self._hs.config.experimental.msc2285_enabled
+            ):
+                continue
             receipt_info = ReadReceipt(
                 receipt.room_id,
                 receipt.receipt_type,