Disconnect all mobile clients when all UI clients leave

Summary: Context https://fb.workplace.com/groups/flippersupport/permalink/1730762380737746/

Reviewed By: lblasa

Differential Revision: D51510348

fbshipit-source-id: afafcdd6b89bf1038fec65a7c3e8c2dd9cfd0768

desktop/flipper-server-core/src/server/attachSocketServer.tsx

@@ -72,6 +72,7 @@ export function attachSocketServer(
     server.emit('browser-connection-created', {});
 
     let connected = true;
+    server.startAcceptingNewConections();
 
     let flipperServerCompanion: FlipperServerCompanion | undefined;
     if (req.url) {
@@ -253,6 +254,10 @@ export function attachSocketServer(
         sessionLength: performance.now() - t0,
       });
 
+      if (numberOfConnectedClients === 0) {
+        server.stopAcceptingNewConections();
+      }
+
       if (
         getFlipperServerConfig().environmentInfo.isHeadlessBuild &&
         isProduction()