RISC-V architecture support

### Is your feature request related to a problem? Please describe.
I would like to know when RISC-V 64 support will be added and what is preventing us from adding it to the .NET SDK (and possibly other dependencies). Some developers have added various hacks to enable RISC-V builds with dotnet, but I am not able to build it on a native RISC-V platform. One issue is that dotnet requires another dotnet to be already available in the system, which I couldn't override through flags while building the main branch. So I had to change the `.dotnet/dotnet-install.sh,` but even then it tries to fetch other dotnet dependencies, and I was not able to override the behavior.

### Describe the solution you'd like
If a lack of CI resources on native RISC-V is causing the upstream of the RISC-V architecture, I can provide the CI with dotnet through a number of [RISC-V compute machines](https://10x-engineers.github.io/riscv-ci-partners/compute_instances/)

Start with .dotnet/dotnet-install.sh and trace the native RISC-V build path described in the issue, including the requirement for an existing dotnet and subsequent dependency downloads. Review how bootstrap behavior is configured and what CI support would require. Done would be a defined, reproducible path for building the .NET SDK on native RISC-V 64, but the issue does not identify specific tests or files beyond the install script.

Written by the indexing model from the issue text.