Track app connections

Summary:
Need to answer:

- How many app connections a day/week?
- How many connections a day/week per app?
- How many connections a day/week per os?
- How many connections a day/week over WWW exchange?
- How many connections a day/week over FS exchange?
- How many connections over a device?
- How many connections over a simulator?

Reviewed By: antonk52

Differential Revision: D46220581

fbshipit-source-id: 6783f49b59cba91cd04625044314973d98cef301

desktop/flipper-server-core/src/utils/tracker.tsx

@@ -18,6 +18,13 @@ type TrackerEvents = {
   };
   'server-socket-already-in-use': {};
   'server-proxy-error': {error: string};
+  'app-connection-created': {
+    app: string;
+    os: string;
+    device: string;
+    device_id: string;
+    medium: number | undefined;
+  };
 };
 
 class ServerCoreTracker {