Handle re-publishing of packages to transport feeds for unstable builds

Migrated from https://github.com/dotnet/core-eng/issues/15344

@markwilkie wrote:

If a package already exists on the transport feed (probably usually happens for VS), add another package identifier to the package so there’s no conflict.

This assumes the root cause is post build signing where we can sign something multiple times

The situation is that because we expose unstable builds to partners (like VS), when a rebuild is required there are downstream challenges because of the immutable package naming in nuget.

Related to https://github.com/dotnet/core-eng/issues/15345