Bugfix: Publish-PSResource should ensure repository.xml file is created before referencing it for dynamic parameters

[anamnavi]

Publish-PSResource has a dynamic parameter and to evaluate it the repository.xml file is referenced by path. However, on a new machine (like a Github runner or fresh image) the file may not exist. So we need to check if that file exists and create it when the dynamic parameter is being set.

PR Summary

PR Context

Resolves #1806

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
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• Breaking changes
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[anamnavi]

closing this in favor of #1868