Find a place to store the repository
Hosting it on GitLab artifacts has problems:
- our repository is already too large and not accepted by GitLab any more
- GitLab artifacts is really slow for many individual files like a flatpak repository.
In the beginning we stored the repository on https://images.plasma-mobile.org/, maybe we could do that again if it's okay to "leak" the authentication token for it to GitLab.com, and if there is enough space.