The objective of this task is to create a loader for Nix/Guix distributions. These distributions expose a `sources.json` containing all sources used at a specific moment.
This work could be split into the following diffs:
1. Create a loader able to load archives: D2792
2. Add a pointer in the snapshot to the commit used to generate the sources.json file
3. Support files that are not archive but plain text.
4. Use all mirrors instead of just the first one.
5. Implement a mechanism to subscribe to a list of `sources.json`.
6. Support others types of source (git for instance)...