Add a remote config option to disable libsignal transport in prod

ts/textsecure/SocketManager.ts

@@ -559,8 +559,14 @@ export class SocketManager extends EventListener {
         : TransportOption.ShadowingLow;
     }
 
-    // in prod, using original
-    return TransportOption.ShadowingLow;
+    // in prod, switch to using 'ShadowingHigh' mode, unless user opts out,
+    // in which case switching to `ShadowingLow`
+    const configValue = window.Signal.RemoteConfig.isEnabled(
+      'desktop.experimentalTransportEnabled.prod'
+    );
+    return configValue
+      ? TransportOption.ShadowingLow
+      : TransportOption.Original;
   }
 
   private connectLibsignalUnauthenticated(): AbortableProcess<IWebSocketResource> {