Contributes to #3739

A join point vertical (identified as DotNetBuildPhase > 1) needs to download packages and assets from previously built verticals. We want to group artifacts and packages together so that downloading and extracting the build artifacts to the right locations is less complex and just requires one download per vertical.

This issue tracks merging the artifacts and packages payload together:

• https://github.com/dotnet/installer/blob/986cd8e87e84681dfa2dc11efa85ce2a2b15176e/eng/pipelines/templates/jobs/vmr-build.yml#L397-L400
• https://github.com/dotnet/installer/blob/986cd8e87e84681dfa2dc11efa85ce2a2b15176e/eng/pipelines/templates/jobs/vmr-build.yml#L366-L369
• https://github.com/dotnet/installer/blob/986cd8e87e84681dfa2dc11efa85ce2a2b15176e/eng/pipelines/templates/jobs/vmr-build.yml#L425-L435