Fix: Nuget PackageEvent

[renardguill]

Resolves #462
Resolves #460

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Before the change?

• The value of Nuget PackageType is nuget (in lowercase)
• The type of NugetMetatada property of PackageVersion is IDictionary<string, dynamic>?

After the change?

• The value of Nuget PackageType is now NUGET (in uppercase) according to the payload sent by GitHub Webhooks.
• The type of NugetMetatada property of PackageVersion is now IEnumerable<PackageVersionNugetMetadata>? according to the paylod sent by GitHub Webhooks and according to the GitHub Webhooks Docs
• Added PackageVersionNugetMetadata type for better binding nuget_metadata field of webhook according to the paylod sent by GitHub Webhooks and according to the GitHub Webhooks Docs

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes
• No

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[github-actions]

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[JamieMagee]

Thanks! I'll cut a release shortly