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 in the gallery repository and review how the Flask application exposes the logged-in username and groups. Follow the Datadog RUM installation guide, coordinate with an RTP for the client and application tokens, and consider the work done when Google Analytics is replaced and the requested logged-in-user context is included.

Written by the indexing model from the issue text.