crates: Create one origin per package instead of per version

Previously we had as many origins as version for a crate package, url was a link
to a specific crate version package.

Refactor to have one origin per package name and add an 'artifacts' entry to
extra_loader_arguments that list all versions, package url and checksum.
Origin url is now a link to the related http api endpoint for a package name.

Related to T4104