[AKS] Support creating windows cluster

[erich-wang]

Description of the new feature

Please refer to detail doc: https://docs.microsoft.com/en-us/azure/aks/windows-container-cli
and implementation in CLI : https://github.com/Azure/azure-cli/blob/dev/src/azure-cli/azure/cli/command_modules/acs/custom.py

Need to clarify

• Configure role assignment of SP to ACR , is it part of implementation?
• Register the WindowsPreview feature and Microsoft.ContainerService namespace (if not already done) => windowspreview until EOY / include dependencies, should be done using separate comdlets?
• Create cluster – with vmss / windows credentials / network-plugin
  network-plugin – API
• Add Windows Server node pool. Kubernetes 1.14.6 min required? (windows stable in 1.14 – no check on cmdlet)

Proposed implementation details (optional)