Add publish to official build

Add publish to official build

This also modernizes publish flow. Each job stores bits in build artifacts, rather than using the dotnetcli blob storage account as an intermediate location.

Some leftover code from ProdCon v1 that was difficult to follow is also removed.

Dev "mock" official builds are also made less risky by accepting override variables and adding a safety that skips official variable groups when the build pipeline name is changed.

Commit migrated from https://github.com/dotnet/core-setup/commit/30f9f19d905ccd63f178af5a326629ad98c73159