Port PyPI lister to the new Lister API

Characteristics of the lister:

• instances: pypi
• base URL: "https://pypi.org/simple/"
• query: none
• state: none
• auth: none
• rate limiting: none "fair use"
• pagination: none
• page format: HTML (minimalist)

Related to swh-scheduler#2442 (closed)

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Migrated from T2956 (view on Phabricator)