Comprehensive Tests for Tag Validation

Related to https://github.com/dotnet/dotnet-docker/issues/2316

This is an epic/tracking issue for the tag validation testing:

- https://github.com/dotnet/dotnet-docker/issues/5838
- https://github.com/dotnet/dotnet-docker/issues/5839
- https://github.com/dotnet/dotnet-docker/issues/5840