Option to keep a downloads cache

In setting up Chocolatey on a GitHub Actions workflow, I configured caching to help speed up installation of my dependencies _MuPDF_ and _ImageMagick.tool_. To this effect, I'm caching `%TEMP%\chocolatey`. However, only the ImageMagick download is being cached. It appears the MuPDF package is deleted from the cache folder as soon as it's installed.

I understand this is due to a difference in how these two package are organized. However, I would like to propose to add an install/configuration option to not delete downloaded packages from the cache dir, so that they can be cached by a CI system.

In any case, thank you for a very useful tool!

Reproduce the GitHub Actions setup with the MuPDF and ImageMagick.tool packages and observe which downloads remain under %TEMP%\chocolatey. Trace the package installation cleanup behavior and identify how an install or configuration option could preserve downloaded packages. Done means the option keeps downloads available for CI caching without changing default cleanup behavior.

Written by the indexing model from the issue text.