Add Azure Key Vault support and enhance credential handling in configuration data

Private/Assert-ConfigurationDataParameterType.ps1

@@ -20,6 +20,11 @@ function Assert-ConfigurationDataParameterType {
 
     switch($TypeName){
         "string" {
+            if(Test-ConfigurationDataSecretReference -Value $Value){
+                Assert-ConfigurationDataSecretReference -Name $Name -TypeName "string" -Value $Value
+                return
+            }
+
             if($Value -isnot [string]){
                 throw "Parameter [$Name] expects type [string], but received [$($Value.GetType().Name)]."
             }