DSC extension needs to be updated to latest API version

[DSC-Extension-IIS-Windows-VM](https://github.com/Azure/azure-quickstart-templates/tree/master/dsc-extension-iis-server-windows-vm)

### Issue Details
Out of date
Should use latest API version and properties for the DSC extension
It's all changed considerably since this version was created.

### Repro steps (*if necessary, delete otherwise*)
n/a

Review the template in the linked DSC-Extension-IIS-Windows-VM directory and compare its DSC extension API version and properties with the current Azure API documentation. Update the template to the latest API and properties, then validate that the template remains deployable.

Written by the indexing model from the issue text.