cpan: Improve listing process by querying the metacpan release endpoint

Instead of querying the metacpan distribution endpoint to list origins,
prefer to use the release endpoint instead enabling to list all artifacts
associated to CPAN packages by scrolling results.

Compared to previous implementation, it enables to compute a last_update
date for all CPAN packages but also to obtain artifact sha256 checksums
that will be used by the CPAN loader to check downloads integrity.

As the multiple versions of a module are spread across multiple pages
from the CPAN API, origins are sent to the scheduler once all pages
processed, it is also faster to proceed that way.

Related to T2833