Homepage > Add user preference option (behind new feature flag) and adjust routing
First step towards &16657 
- Add new wipfeature flag behind which we can build the new homepage.
- Behind this FF, allow to set user preference to new homepage.
- Adjust routing to allow this.
I drafted parts of this (and other stuff) in !192639 (closed) and will extract a clean MR for these basics.
Edited  by 🤖 GitLab Bot 🤖