Ingest Julia packages

Summary:

The Julia ecosystem contains over 9,000 packages that are registered in the General registry, which means that finding the right package can be a challenge. Fortunately, there are services that can help navigate the ecosystem, including:

Plan:

• swh/devel/swh-lister!489 (merged): Implement lister
• docker: Run lister [1]
• Implement loader No need, it's origin with type 'git'
• swh/devel/swh-lister!507 (merged): Implement incremental lister
• docker: Run incremental lister ^
• docker: Run loader
• Document lister
• Document loader
• Deploy on staging
• Call for public review
• Deploy on production

[1] swh/devel/swh-lister!489 (comment 151944)