redirects for Databased Backed Blacklists

[graingert]

What's the problem this feature will solve?
currently you run pip install requirements.txt or pip install pip-sync and pip fails with no useful advice

Describe the solution you'd like
pypi should provide advice for each blacklisted package eg
requirements.txt -> "you should use -r requirements.txt"
pip-sync -> "you should install pip-compile"
bad-package-with-virus -> "this package was removed because it was malicious"

Where redirecting to a package the HTTP interface should also redirect to the new package

Additional context
graingert/pip-compile#1

[graingert]

somewhat like https://docs.npmjs.com/cli/deprecate

[di]

I think this makes more sense as a feature request for pip, similar to pypa/pip#5777, which would also be blocked on implementing #4703.