Archive loader should have a snapshot append mode
In a near future, Software Heritage ambassadors will be able to submit save code now requests with a new
archives visit type from the Web UI.
That visit type will allow to load multiple tarballs or zip files under a same software origin, one branch being created for each artifact to load.
Under the hood, the ArchiveLoader is used to load the tarballs into the archive.
However, that loader creates a new visit with a snapshot containing only the given tarballs provided as parameter each time it is invoked.
For the save code now case, it means that if a user submits a first request for an origin with a given set of artifacts and then another one with a different set of artifacts, he will have to switch between visits to access all the code loaded into the archive.
It would be much more convenient to include all artifacts previously uploaded in any new snapshot created by the loader, thus any artifacts uploaded so far will be available in the latest snapshot of the origin.
This could be implemented by adding a new option to the loader.
Migrated from T3347 (view on Phabricator)