PyPi: Support package installation

Details

Package installation is done using the Legacy Simple API.

Sample command:

python3 -m pip install --index-url https://test.pypi.org/simple/ --no-deps <package-name>

This command makes 2 request, the first is a GET /simple/<package-name>, which returns a HTML with links to the packages for each version. The second request is simply a GET to download the proper distribution file.

A sample request and response can be found in the docs.

Entry Points

GET gitlab.com/api/v4/projects/:id/packages/pypi/simple/<package-name>: The entry point to get the meta data about the package with the list of versions and files to download.

GET gitlab.com/api/v4/packages/pypi/<file-identifier>: The url to download the package file.

Authentication

Needs to support Authentication via basic HTTP auth to allow for either CI tokens or PAT.

See #34161 (closed) for full discussion.