Tasks needed for .NET 9 GA

[lbussell]

• [ ] Move latest tags in manifest.json to the new version - Relevant issue: https://github.com/dotnet/dotnet-docker/issues/2316
• [ ] Add the new .NET version to the .NET Framework SDK image
  • https://github.com/microsoft/dotnet-framework-docker/blob/6a3c9d048f75c1e69c0e1059564cd56a90bf9e3c/eng/dockerfile-templates/sdk/Dockerfile#L56-L59
• [ ] Post a new announcement on the GitHub Discussions page page and pin the announcement
  • Include new .NET Docker features and breaking changes and defer to other official .NET documentation/announcements for other features
  • Example announcement: https://github.com/dotnet/dotnet-docker/discussions/4995
• [ ] Update documentation as necessary to reference the new .NET version

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