NuGet Runtime pack for community-supported architectures

### Is your feature request related to a problem? Please describe.

.NET now has a few community-supported platforms: `linux-riscv64`, `linux-loongarch64`, etc.

And to properly support cross-publishing in .NET SDK, we need to get runtime packages from NuGet, otherwise publish will fail.

Hosting these packages on self-hosted repos are certainly an option, but is it possible now for maintainers to push those to NuGet.org under their own account? (Not as Microsoft because they won't be supported by Microsoft to begin with).

That way we can get a consistent publish experience.