[Fixes] Update VM domainJoin parameter usage

[jriekse5555]

Readme PR per request by Rainer Halanek PR related to bug I submitted (#1595). Updated the domain join settings to the correct ones to domain join correctly. The previous ones in the readme do not work and would attempt to join a blank workgroup. Reference: https://docs.microsoft.com/en-us/azure/active-directory-domain-services/join-windows-vm-template

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[ahmadabdalla]

Thanks for the contribution @jriekse5555