Support legacy repository fall back redirects

[neilvana]

Pull Request Check List

• Added tests for changed code.
• Updated documentation for changed code.

Legacy repositories may specify a fallback url if a package is contained in an upstream repository. To support this redirection we should use the url contained in the response when creating a Page object to ensure relative links are properly calculated.

[thejcannon]

@abn (sorry couldn't find out how to mention the triage) anything the community can do to get this along?

This is basically the only missing piece to having us roll out poetry to all the tools at our company. We're all very eager to abandon our tox+requirements+setup.py solution for poetry ❤️

[sinoroc]

Looks like it is the same issue as #3293 and looks like it is the same fix as suggested in #3198.

Maybe the authors of both PRs can agree on something here.

[neilvana]

I've left comments on #3198. I plan to discard this PR if that one is accepted.

[neilvana]

Since progress is being made in #3198 I'm closing this PR in favor of that one.

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.