Refactor swh module to computes canonical github origins

Reusing the swh.core.github.utils.GitHubSession class.

Extra plan:

• Refactor swh.web to canonicalize the gh origin server side
• Adapt packagist lister
• Adapt remaining listers if any
• Adapt nixguix loader (or lister if it got refactored prior to this)

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Migrated from T4279 (view on Phabricator)

mentioned in issue #4232 (closed)

marked this issue as related to #4232 (closed)

added Lister priority:Normal labels