Add Save-ChocolateyPackage function

[gaelcolas]

As per https://docs.chocolatey.org/en-us/choco/commands/download this is a Choco pro/pro+ feature.

This needs to be added to the Chocolatey module (currently hosted in Chocolatey-Community org).

The goal is to have a Save-ChocolateyPackage function (or a better name for it) so that we can download a package, in the hope to push it to another Repository.

It would be great to gracefully handle dependencies (i.e. ignore or download if missing from destination folder).

A fair bit of work here will be to setup the pipeline and tests for it.

[gaelcolas]

https://dsccommunity.org/blog/convert-a-module-for-continuous-delivery/