Currently, loading Nix and Guix as single origins with a huge snapshot, with each branch name being a URL is wrong.
We need to replace the Nixguix loader with a lister, which creates as many origins referenced by Nix and Guix public manifests.
This would be closer to what we do with Debian/Ubuntu.
TODO, define the following:
- [ ] target structure sketch of the data in the archive
- [ ] What are the origin urls?
- [ ] what kind of extrinsic metadata and/or extids are we storing?
- [ ] what kinds of snapshots we're generating