ChefExtension support in the azure sdk toolkit

Contribution to the Azure SDK Toolkit from Chef - To support ChefExtension cmdlets.
Note - ClogenyTechnologies has a contract with Chef. We have signed the Microsoft CLA. This new PR has been created to accomodate the "rebase" after this repo had been restructured.
Original PR - https://github.com/Azure/azure-sdk-tools/pull/2576
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