Publish all supported images to the non-core branded repositories

[MichaelSimons]

For .NET 5.0 a new set of non-core branded repositories were created. See this announcement for details. The original plan was to publish all 5.0 and higher images to the new mcr.microsoft.com/dotnet repos and continue publishing the 3.1 and 2.1 images to the existing mcr.microsoft.com/dotnet/core repos.

This presents some challenges for our customers in certain scenarios. If they have automation/tooling/infra around the .NET repositories, they may have to add conditional logic that inspects version numbers to know which .NET repos to target. If all of the .NET images were published to the new non-core repos, it would eliminate the need for this conditional logic. Customers could make a complete switch to use the new repos. This would be similar to what was done during the transition from publishing the .NET images on DockerHub to MCR.

[MichaelSimons]

To further improve the UX, we should redirect users from the "core" branded repositories on Docker Hub to the new repositories. The "core" branded repositories should no longer get indexed and appear in the Docker Hub search results. This will simplify the number of choices our customers have to pick from when searching for .NET images.