Adds some settings to check flipper-server state

Summary:
There's one setting: to enable or disable flipper-server.

However, I've added some current running state to it. If there's a better way of doing this, please do let me know.

Reviewed By: aigoncharov

Differential Revision: D37276670

fbshipit-source-id: f6c941cf0cfe55c267b9bcb9f799934fba1e28ef

desktop/flipper-server/src/index.tsx

@@ -105,6 +105,7 @@ async function start() {
     argv.settingsString,
     argv.launcherSettings,
     keytar,
+    'external',
   );
   const companionEnv = await initCompanionEnv(flipperServer);
   if (argv.failFast) {