PEP-0691 format query parameter does not remain after redirect

[Wouterkoorn]

The current implementation of PEP-0691 gives some unfriendly redirect behavior when browsing with the format query parameter. If you omit the trailing slash, it redirects without keeping the query parameter.

https://pypi.org/simple/pip redirects to https://pypi.org/simple/pip/
https://pypi.org/simple/pip?format=application/vnd.pypi.simple.v1+json does not redirect to https://pypi.org/simple/pip/?format=application/vnd.pypi.simple.v1+json

Although it might not be a standardized requirement, it is friendly to have.

[dstufft]

This will be because we strip the format parameter from the request at the edge, and translate it into an Accept header.

It's probably dependent on #11558

[di]

Marking this as blocked on #11558.