Start Flipper HTTP server even if app server fails to start

Summary:
**Issue**
From passy:
when one of the app server ports is occupied, Flipper PWA is stuck at the loading screen

Reviewed By: passy

Differential Revision: D50261985

fbshipit-source-id: 8ce90cd6d515c26a824645f642dacbe92e7f4105

desktop/flipper-server/src/index.tsx

@@ -243,7 +243,9 @@ async function start() {
       }
     });
   }
-  await flipperServer.connect();
+  await flipperServer
+    .connect()
+    .catch((e) => console.warn('Flipper Server failed to initialize', e));
 
   const t8 = performance.now();
   const appServerStartedMS = t8 - t7;