Use auth token when connecting to existing server from Electron

Summary:
All clients need to provide an authentication token before connecting. Electron app is no different.

This change adds the authentication token whether we are connecting over UDS or TCP.

Before this change, if Flipper server was already running, launching the Electron app would look similar to this:

{F1016961594}

Reviewed By: antonk52

Differential Revision: D46418758

fbshipit-source-id: f00ffe675df78403d5921250e3e9ed9331a55bde

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

@@ -22,4 +22,4 @@ export {isFBBuild} from './fb-stubs/constants';
 
 export {WEBSOCKET_MAX_MESSAGE_SIZE} from './comms/ServerWebSocket';
 
-export {getAuthToken} from './utils/certificateUtils';
+export {getAuthToken, hasAuthToken} from './utils/certificateUtils';