Backport #24098

This pull request includes various updates to the build and CI configuration to support switching between public and private NuGet feeds, as well as some documentation updates. The most important changes include the addition of a Switch-PSNugetConfig function, modifications to the Start-PSBuild and Start-PSPester functions to support a new -UseNuGetOrg parameter, and updates to the CI pipeline scripts to switch to public feeds.

Build and CI Configuration Updates:

• Added Switch-PSNugetConfig function to switch between public and private NuGet feeds in build.psm1.
• Updated Start-PSBuild and Start-PSPester functions to support a new -UseNuGetOrg parameter for using nuget.org instead of the default feeds. [1] [2]
• Modified CI pipeline scripts to switch to public feeds using Switch-PSNugetConfig function. [1] [2]

Pipeline Template Changes:

• Updated .pipelines/templates/insert-nuget-config-azfeed.yml to use a NugetPackageSource object for specifying NuGet feed URLs. [1] [2]
• Added a step in windows-packaging.yml to switch to public feeds during the CI build.

Documentation Updates:

• Updated various documentation files to reflect the new -UseNuGetOrg parameter for Start-PSBuild and Start-PSPester. [1] [2] [3] [4] [5] [6] [7]
• Removed outdated nuget.config creation instructions from docs/host-powershell/sample/NuGet.config.md.

These changes aim to streamline the build process and ensure consistency across different environments by allowing easy switching between public and private NuGet feeds.