The branch points to the commit used to generate the list of
sources. This revision may not exist in software heritage but we know
the git loader will create it;)

This method allows to add extra branches before creating the snapshot.

This loader is in charge of loading sources of Nix/Guix
evaluations. These sources are listed in a JSON file which is ingested
by this loader.

- Disk routine is done through a cron that cleans up regularly temp folders
- previous commit fixes the second part about from_disk adaptations

PackageLoader.load() was way too long and nested.

swh-storage >= v0.0.174 requires swh-model objects in other proxies,
so the validation proxy must be before the other ones.

Required by swh-storage >= v0.0.172.

Also use swh.model objects to ease the conversion.

Instead of failing the ingestion, this will allow ingestion of further
artifacts.

Related https://sentry.softwareheritage.org/share/issue/769f9b19f2f54e939cc7f163844bd95c/

Instead of failing the ingestion with unclear reasons, raise a more explicit
message. This will allow us to know whether this case is frequent or not.

Related to [1]

[1] https://sentry.softwareheritage.org/share/issue/8773eb3140b94675a08143935a61087c/

Related to [1]

[1] https://sentry.softwareheritage.org/share/issue/4a2d3c5f6d4942ddb94a68bb532b6d02/

Also align that behavior for directory

See [1] for an error instance.

[1] https://sentry.softwareheritage.org/share/issue/b3d7333ec47745f7a5fcdc951d5fc6ab/

Related to T2188

It's no longer needed as git and mercurial loaders using those have been
migrated to the new names.

Prior to this commit, the origin url was targeting solely one versioned
artifact. This adaptation allows to have a canonical url as origin to which we
associate a list of artifacts to ingest (symmetrically as what is done for
other package loaders).

Related to D2524

This is setup-ed through configuration using the proxy storage.

Use directly self.storage.origin_* endpoints

The only loader initially using this was the old loader deposit implementation.
The new one implements it on its own.

This commit fixes unicode error raised during DESCRIPTION file parsing.