[Feature] Allow Environment Override

[avi-jois]

Allow the pip environment used for evaluating environment markers to be overriden, so requirements can be compiled for an environment different than the user's current environment.

Contributor checklist

• [X] Provided the tests for the changes.
• [X] Assure PR title is short, clear, and good to be included in the user-oriented changelog

Maintainer checklist

• [ ] Assure one of these labels is present: backwards incompatible, feature, enhancement, deprecation, bug, dependency, docs or skip-changelog as they determine changelog listing.
• [ ] Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).

[avi-jois]

@aignas Thanks for the comments! I made some updates based on your feedback, let me know if there are any remaining concerns you have.

@atugushev I saw you are one of the leads on this project, do you think this feature makes sense?