Add environment variable to always use --active flag

[albireox]

Summary

The new --active flag (#11189) is a great addition and I think it goes some way to allow uv and pyenv to work better together (see #6204).

Would it be possible to add a new environment variable to make that flag the default? For example, the PR suggested something like UV_PROJECT_ENVIRONMENT=ACTIVE but could also be UV_ACTIVE=1. Or maybe this already works? If so, it's not clear from the documentation.

Example

No response

[zanieb]

I posted some ideas in #11189 (comment) but did not add one yet. I'm not sure what name is best.

[albireox]

I think any of the options in that comment would work. My personal preference would be a new variable, so something like UV_PROJECT_USE_ACTIVE.