Review APIs to get metadata from supported origins

Before deciding on an architecture to fetch extrinsic metadata, we need to know what APIs are available to us to fetch them.

for all forges/package-managers/... we have listers for:

• bitbucket
• cran
• debian
• github
• gitlab
• gnu
• npm
• phabricator
• pypi

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Migrated from T1747 (view on Phabricator)