Migrate to .NET 10

[yselkowitz]

Review request: https://bugzilla.redhat.com/show_bug.cgi?id=2397031

Once added to rawhide, it should be added to ELN, and dotnet8.0 and dotnet9.0 dropped therefrom (but not from CS).

Also, with the recent announcement that STS releases will receive 24 months of upstream support (expiring at the same time as the previous LTS), only the latest version of .NET should ever be needed in ELN.

[yselkowitz]

Bootstrap build is tagged in eln-build-side-120472.