feat((rn,config) add a/b test flag to enable XMPP WebSockets on mobile

config.js

         // disabled by the below option.
         // enableThumbnailReordering: true,
 
+        // Enables XMPP WebSocket (as opposed to BOSH) for the given amount of users.
+        // mobileXmppWsThreshold: 10 // enable XMPP WebSockets on mobile for 10% of the users
+
         // P2P test mode disables automatic switching to P2P when there are 2
         // participants in the conference.
-        p2pTestMode: false
+        // p2pTestMode: false,
 
         // Enables the test specific features consumed by jitsi-meet-torture
         // testMode: false

react/features/base/connection/actions.native.js

     // redux store.
     const options = _.cloneDeep(state['features/base/config']);
 
-    let { bosh } = options;
-    const { websocket } = options;
+    let { bosh, websocket } = options;
+
+    // TESTING: Only enable WebSocket for some percentage of users.
+    if (websocket) {
+        if ((Math.random() * 100) >= (options?.testing?.mobileXmppWsThreshold ?? 0)) {
+            websocket = undefined;
+        }
+    }
 
     // Normalize the BOSH URL.
     if (bosh && !websocket) {
     // WebSocket is preferred over BOSH.
     const serviceUrl = websocket || bosh;
 
+    logger.log(`Using service URL ${serviceUrl}`);
+
     // Append room to the URL's search.
     const { room } = state['features/base/conference'];