Gg/cmake from local files

[gegorohoff]

Pull Request Description

Hey Scott, in one of our workflows, a warning from the download_step (and in downloader.__unpack()) within generic_cmake.__setup() was getting slurped into the dockerfile. I'm working with Adam to not pull in STDERR into the dockerfile as its not necessary but I thought this update might still be valuable for users who are copying a directory into their image like myself.

The update is simply exposing the download_step's unpack kwarg as an option to generic_cmake "unpack_download".

If there is already a supported way to do this, I'm happy to hear about it.

Author Checklist

• [X] Updated documentation (pydocmd generate) if any docstrings have been modified
• [X] Passes all unit tests