✨(frontend) integrate posthog analytics

We integrate posthog, it will help us to track
user behavior and improve the product.
We get the configuration from the backend config
endpoint.

src/frontend/apps/e2e/__tests__/app-impress/config.spec.ts

@@ -16,6 +16,7 @@ const config = {
     ['de-de', 'German'],
   ],
   LANGUAGE_CODE: 'en-us',
+  POSTHOG_KEY: {},
   SENTRY_DSN: null,
 };