Port #4086 to 1.1 branch

[robin92]

Resolves: #3216

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

[robin92]

Poetry 1.1.13 has issues with downloading packages from private PyPI servers hosted on Azure Artifacts. Problem manifests with a HTTP 401 Unauthorized error and seems to already have been reported and handled by #4086. However, that PR targets the master branch and next feature release but users of current stable releases are left with effectively no access to Azure Artifacts.

This PR ports the change made by @Darsstar to 1.1 branch along with some pip.py file and ephemeral_environment function from other commits (dependencies). This change has been tested on the Azure Artifacts PyPI server I have access to and it works.

TODOs:

• correct ported function name in commit message
• make pipeline pass

[Secrus]

Poetry team has no plan for another 1.1.x release, so it won't be backported.

[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.