[Feature request] Track files that have been downloaded for a package

[flcdrg]

As a package maintainer, I want to be able to write scripts that can interact with the individual files that have been downloaded by chocolatey-au (as part of calculating checksums).

One example use for this is to be able to submit the files to VirusTotal, like I do in https://github.com/flcdrg/au-packages/blob/master/_scripts/Submit-VirusTotal.ps1