Add .NET 11 images

[lbussell]

Fixes #6824

Initial operating systems in this PR:

• Ubuntu 26.04 (Resolute)
• Alpine 3.23
• Azure Linux 3.0
• Nano Server 2025
• Windows Server 2025

This will fail pre-build validation until #6869 is merged because that PR contains the ImageBuilder update that adds Ubuntu 26.04 (Resolute) support.

[lbussell]

Project templates are missing for .NET 11 which is causing the tests to fail.

   System.InvalidOperationException : Failed to execute docker run --name 11.0-create-web-134100360290570382 -w /app --platform linux/amd64 mcr.microsoft.com/dotnet/nightly/sdk:11.0-preview-alpine3.23-aot-amd64 dotnet new web --framework net11.0 --no-restore --exclude-launch-settings
Exit code: 127
Standard Error: No .NET SDKs were found.

Download a .NET SDK:
https://aka.ms/dotnet/download

Learn about SDK resolution:
https://aka.ms/dotnet/sdk-not-found
Error: Invalid option(s):
--framework net11.0
   'net11.0' is not a valid value for --framework. The possible values are:
      net10.0   - Target net10.0

For more information, run:
   dotnet new web -h

/cc @baronfel is there a tracking issue for updating the templates?

[baronfel]

It's one of the line items in dotnet/sdk#50295, yes.

[richlander]

This seems like it could be managed as an array of options. In theory, we could test all supported .NET versions with dotnet new. We merge this PR w/just .NET 10 for now.

[lbussell]

This seems like it could be managed as an array of options. In theory, we could test all supported .NET versions with dotnet new. We merge this PR w/just .NET 10 for now.

Yes, I see many ways we can improve our unit tests. I think we can improve things incrementally after this PR is merged.