Update nuget.config to use CFS feed

[adityapatwardhan]

PR Summary

Update the nuget.config file to use a CFS feed.

PR Context

PR Checklist

• [ ] PR has a meaningful title
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• [ ] Summarized changes
• [ ] Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
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• Breaking changes
  • [ ] None
  • OR
  • [ ] [Documentation needed]()
    • [ ] Issue filed:
• User-facing changes
  • [ ] Not Applicable
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  • [ ] [Documentation needed]()
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• Testing - New and feature
  • [ ] N/A or can only be tested interactively
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  • [ ] Make sure you've added a new test if existing tests do not effectively test the code changed
• Tooling
  • [ ] I have considered the user experience from a tooling perspective and don't believe tooling will be impacted.
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  • [ ] I have considered the user experience from a tooling perspective and enumerated concerns in the summary.