Track usage with Datadog RUM

Replace Google analytics with Datadog RUM

See https://www.datadoghq.com/rum/ for a description
Follow the setup guide: https://docs.datadoghq.com/real_user_monitoring/installation/?tab=us
Make sure to include information about logged in users, for example
```javascript
datadogRum.addRumGlobalContext('usr', { // usr as defined in the datadog naming guide https://docs.datadoghq.com/logs/processing/attributes_naming_convention/#user-related-attributes
uid: username,
groups: groups // If available
});
```

Reach out to an RTP for client and application tokens

Start by locating the existing Google Analytics integration and the application entry point, then follow the Datadog RUM setup and user-attribute links in the issue. Done means Google Analytics is replaced, logged-in user context is included where available, and the required client and application tokens have been obtained from an RTP.

Vom Indexierungsmodell aus dem Issue-Text verfasst.