Provide a mechanism to gather prereq packages required to run smoke-tests offline

[MichaelSimons]

The smoke-tests do not support running offline as they have a set of prereq packages. The source-build infrastructure should provide a mechanism to gather these packages so that the tests can be run offline.

The prep script script feels like the natural place for this to happen as it's primary responsibility is to gather the prereqs necessary to build.

[mthalman]

During development of dotnet/installer#16359, it became clear that versions of dependent packages are being updated frequently enough that makes the maintenance of a baseline file unsustainable.

For that reason, a different approach needs to be taken. Rather than relying on the prep script that would need to be run to gather the smoke test prereqs, the proposal is that a tarball containining these prereqs is provided as part of the release assets. This tarball would contain all the necessary packages for building and running the smoke tests offline. It would need to consolidate all of the restored packages from the various architectures of build legs since there are architecture-specific packages included in the mix.

[mthalman]

@omajid / @mirespace - Please read the new approach I've described in #3386 (comment) and let me know your thoughts. Feel free to respond here if further clarification is needed.

Fundamentally, this isn't much different than what we do today for partner hand-off. This will just be automated as part of our release process. And the tarball that is produced will only include packages that are consumed by the smoke tests. Previously, we had been including some additional packages that weren't necessarily consumed by our smoke tests; those will no longer be included if the tests don't need them.

[omajid]

Hey, @mthalman ! I don't think we (Red Hat) use the tarballs anymore. We use the nuget feed directly, along with something similar to https://github.com/dotnet/source-build/blob/b9be5fbf2a037a002713bcb4ffec6527e1520425/test/GatherPackages.csproj#L13C1-L21, to download all the packages we need.