Display env vars for pip options in docs

[ctg123]

Ref #8044

[uranusjr]

Need to fix errors in CI. I also wonder there should be a link to the environment variable documentation. https://pip.pypa.io/en/stable/topics/configuration/#environment-variables

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Example rendering, for reviewers: https://pip--11993.org.readthedocs.build/en/11993/cli/pip_install/#options

[pradyunsg]

I also wonder there should be a link to the environment variable documentation. pip.pypa.io/en/stable/topics/configuration/#environment-variables

Let's get this landed, and then we can improve this in a follow up! :)

[pradyunsg]

@ctg123 Could you look into the code style checks mentioned in https://results.pre-commit.ci/run/github/1446467/1682204558.lnkhmFhyTr-BUqnOYSGFmw?

You can run those checks locally as documented in https://pip.pypa.io/en/stable/development/getting-started/#running-linters

[ctg123]

Hi all, OK I will look into running the CI tests this week.

[webknjaz]

@ctg123 looks like beside autoformatting, you'd need to add some typing as well. But feel free to add separate commits, one fix at a time if that's easier.

[webknjaz]

Context: this PR was created during https://us.pycon.org/2023/events/mentored-sprints/. It may need somebody to take over and polish the types for linting to pass. This can be done through a separate PR — somebody would need to git fetch https://github.com/ctg123/pip/tree/docs-envvars.git in their fork and then do something like git checkout -b maintenance/11993/docs-env-vars-rendering docs-envvars to get the original commits from this PR and make another branch+PR with those included.

[luismedel]

Context: this PR was created during https://us.pycon.org/2023/events/mentored-sprints/. It may need somebody to take over and polish the types for linting to pass. This can be done through a separate PR — somebody would need to git fetch https://github.com/ctg123/pip/tree/docs-envvars.git in their fork and then do something like git checkout -b maintenance/11993/docs-env-vars-rendering docs-envvars to get the original commits from this PR and make another branch+PR with those included.

@webknjaz I created a new PR including this and the missing changes.