Even though the implementation is not complete , we can deploy a first version
of the loader which can already ingest the majority of artifacts.
This will most likely creates partial snapshot most of the time but that's
still snapshot that are browsable from the archive.
We can thus deploy it.
This task tracks the actions to do so.
- D3165: Update puppet manifests (only staging is referenced for now).
- Deploy on workers
- Register task-type load-nixguix in scheduler 
- Schedule origins to ingest the following sources.json 
striken sources are deactivated for now (seen with @lewo).
 As the parent task mentions, for now, some artifacts are not dealt with (they
have been mostly filtered out in the sources.json for now)
 Idempotently register new task-types (out of new version of loader
packages, noop on existing ones)
SWH_CONFIG_FILENAME=/etc/softwareheritage/scheduler.yml swh scheduler --config-file $SWH_CONFIG_FILENAME \ task-type register \ --plugins loader.nixguix
 Scheduling task (on the right scheduler)
swh scheduler --config-file $SWH_CONFIG_FILENAME \ task add load-nixguix \ url=https://nix-community.github.io/nixpkgs-swh/sources-unstable.json