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: D2807
3. Support files that are not archive but plain text: D2854
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)...