Cannot convert value to type System.String.

### dsc-extension-iis-server-windows-vm

https://github.com/Azure/azure-quickstart-templates/tree/master/dsc-extension-iis-server-windows-vm
### Issue Details

DSC gives the following error during deployment in Azure:

**Cannot process argument transformation on parameter 'ConfigurationFunction'. Cannot
convert value to type System.String.**

Other parameters are working fine and when I hardcode the following text in the JSON template, it works fine: "IISWebsite.ps1\IISWebsite"

I use the JSON file in the following way:
- PowerShell Runbook 1: The user runs this runbook that runs two other runbooks:
- PowerShell Runbook 1.1: Create a Resource Group. This script creates a new resource group
- PowerShell Runbook 1.2: Create a VM with DSC extension. This script uses the JSON template.

So the user provides the value of the parameter in Azure at Runbook 1:

```
# Choose the Configuration Function
[Parameter(Mandatory=$true)]
[String]$configurationFunction,
```

That goes to Runbook 1.2:

```
# Choose the Configuration Function
[Parameter(Mandatory=$true)]
[String]$configurationFunction,
```

To the following JSON parameter:

```
"configurationFunction": {
"type": "string",
"defaultValue": "IISWebsite.ps1\\IISWebsite",
"metadata": {
"description": "DSC configuration function to call"
}
},
```

To configure the DSC properties in the JSON template:

```
"properties": {
"publisher": "Microsoft.Powershell",
"type": "DSC",
"typeHandlerVersion": "2.19",
"settings": {
"ModulesUrl": "[parameters('modulesUrl')]",
"ConfigurationFunction": "[parameters('configurationFunction')]",
"Properties": {
"MachineName": "[parameters('vmName')]"
}
},
"protectedSettings": null
}
```

Start with the dsc-extension-iis-server-windows-vm template and trace configurationFunction from PowerShell Runbook 1 through Runbook 1.2 into the JSON DSC settings. Compare the parameterized value with the hardcoded IISWebsite.ps1\\IISWebsite value and reproduce the deployment error. Done means identifying why the parameter is not accepted as a string and documenting or correcting the template flow.

Written by the indexing model from the issue text.