[ASPNETCORE] Add/improve support for .NET 8-10

[MisinformedDNA]

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Summary by cubic

Modernized the ASP.NET Core server generator for .NET 8–10. Adds minimal-hosting templates and presets for 9.0/10.0, plus CI to build the new samples.

• New Features

  • Added aspnetcore/8.0 templates with minimal hosting (Program.mustache), no Startup, new auth/filters/formatters, and OpenAPI helpers.
  • Updated project templates to include Nullable and ImplicitUsings; added new Dockerfile templates using mcr.microsoft.com/dotnet/aspnet and mcr.microsoft.com/dotnet/sdk with ports 8080/8081.
  • Introduced config presets for 9.0 and 10.0 (base, NewtonsoftFalse, nullableReferenceTypes, pocoModels, project4Models, useSwashBuckle, use-centralized-package-version-management) pointing to the new 8.0 templates.
  • Added GitHub Actions workflows to build .NET 9 and 10 sample servers.
  • Regenerated the .NET 8 petstore sample to use minimal hosting and the new Docker image/port setup.

• Migration

  • Regenerate ASP.NET Core servers with aspnetCoreVersion set to 8.0, 9.0, or 10.0 and templateDir set to modules/openapi-generator/src/main/resources/aspnetcore/8.0.
  • Remove Startup.cs; the new output uses top-level Program.cs with minimal hosting.
  • Update containers to use mcr.microsoft.com/dotnet/aspnet and mcr.microsoft.com/dotnet/sdk and switch exposed ports from 80/443 to 8080/8081.
  • If you mapped old ports in deployment, adjust ingress/service mappings accordingly.

^{Written for commit 0a2adfc. Summary will update on new commits.}