Add more tracking data for UI startup

Reviewed By: lblasa

Differential Revision: D50365803

fbshipit-source-id: b6a601e7bf987738400a86be6814de7cafd50d3d

desktop/flipper-ui-browser/src/global.tsx

@@ -18,6 +18,8 @@ declare global {
     };
     GRAPH_SECRET: string;
     FLIPPER_APP_VERSION: string;
+    FLIPPER_SESSION_ID: string;
+    FLIPPER_UNIXNAME: string;
 
     flipperShowMessage?(message: string): void;
     flipperHideMessage?(): void;