Updated models to handle nullable and make events properties readonly

[navali-msft]

All SDK Contribution checklist:

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• Please open PR in Draft mode if it is:
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  • Encountering multiple pipeline failures and working on fixes.
• If an SDK is being regenerated based on a new swagger spec, a link to the pull request containing these swagger spec changes has been included above.
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Testing Guidelines

• Pull request includes test coverage for the included changes.

SDK Generation Guidelines

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Additional management plane SDK specific contribution checklist:

Note: Only applies to Microsoft.Azure.Management.[RP] or Azure.ResourceManager.[RP]

• Include updated management metadata.
• Update AzureRP.props to add/remove version info to maintain up to date API versions.

Management plane SDK Troubleshooting

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  Note: We have recently updated the PSH module called by generate.ps1 to emit additional data. This would help reduce/eliminate the Code Verification check error. Please run following command:

    `dotnet msbuild eng/mgmt.proj /t:Util /p:UtilityName=InstallPsModules`
  

Old outstanding PR cleanup

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