ACR Integration: Add JSON metadata to package manifest in ACR registries

[alerickson]

PR Summary

Add metadata JSON string to package manifest in ACR registries.

PR Context

Resolves #1515

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
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  • [ ] [Documentation needed]()
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• User-facing changes
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  • [ ] [Documentation needed]()
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• Testing - New and feature
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  • [ ] Make sure you've added a new test if existing tests do not effectively test the code changed
• Tooling
  • [x] I have considered the user experience from a tooling perspective and don't believe tooling will be impacted.
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