Enable shipping images without platform-specific tags

[lbussell]

Currently, there are build/publish errors when we try to ship images that do not contain any platform-specific tags and only contain multi-platform tags/manifest list tags. We should investigate what those errors are and fix them so that we can remove arch-specific tags for appliance images (dotnet/dotnet-docker#6053).

[ghost]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[ghost]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.