Implement Group Policy settings for PSResource Repository

[adityapatwardhan]

PR Summary

Implement Group Policy settings for PSResource Repository. Policy allows administrator to define an allow list for Uris that are allowed to be used for finding and installing resources.

The format for the policy is as follows:

Name=PSGallery;Uri=https://www.powershellgallery.com/api/v2/

PR Context

Fixes #1696

PR Checklist

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• [x] Summarized changes
• [x] Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
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• Breaking changes
  • [x] None
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  • [x] [Documentation needed]()
    • [X] Issue filed: https://github.com/MicrosoftDocs/PowerShell-Docs-PSGet/issues/163
• User-facing changes
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  • [ ] [Documentation needed]()
    • [ ] Issue filed:
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