Add support for .env file

[jmariller]

Hi,

I am referring to an already existing issue which was closed, imho, without a proper resolution: https://github.com/yarnpkg/berry/issues/2724

There was a pull request which was eventually rejected, with a proposed alternative solution (see one of the first messages from @paul-soporan): https://github.com/yarnpkg/berry/pull/3938

Now I would really love to try and implement the proposal myself, unfortunately I do not have enough time and knowledge on my end. However with some hints and support I would be more than happy to help: is anybody willing to support this?

Many thanks!