Add extensions functionality for C# refactor

[tevoinea]

Summary of the Pull Request

What is this about?

Related to migrating timer_repro.

Highlights of changes:

• Added ImageOperations which is used for working with VM images.
• Made generic wrapper type over VirtualMachineScaleSetExtensionData and VirtualMachineExtensionData. We use the same extensions (and same extension properties) for both and since I can't add a shared interface between the types ( and instead of duplicating the extension configuration functions), I created VMExtensionWrapper.
• Fixed some bugs in the existing extensions functions (ex: making sure our types are serialized as Azure expects, a couple of missing awaits)

PR Checklist

• Applies to work item: [Refactor] timer_repro to C# #1837