bicep/matrix: add synapse config to help with livekit

hosts/bicep/services/matrix/synapse.nix

@@ -95,6 +95,32 @@ in {
         }
       ];
 
+      experimental_features = {
+        # MSC3266: Room summary API. Used for knocking over federation
+        msc3266_enabled = true;
+        # MSC4222 needed for syncv2 state_after. This allow clients to
+        # correctly track the state of the room.
+        msc4222_enabled = true;
+      };
+
+      # The maximum allowed duration by which sent events can be delayed, as
+      # per MSC4140.
+      max_event_delay_duration = "24h";
+
+      rc_message = {
+        # This needs to match at least e2ee key sharing frequency plus a bit of headroom
+        # Note key sharing events are bursty
+        per_second = 0.5;
+        burst_count = 30;
+      };
+
+      rc_delayed_event_mgmt = {
+        # This needs to match at least the heart-beat frequency plus a bit of headroom
+        # Currently the heart-beat is every 5 seconds which translates into a rate of 0.2s
+        per_second = 1;
+        burst_count = 20;
+      };
+
       trusted_key_servers = [
         { server_name = "matrix.org"; }
         { server_name = "dodsorf.as"; }