Enhance configuration data validation and add new utility functions

- Added validation for empty values in Assert-ConfigurationDataParameter.
- Introduced Assert-ConfigurationDataSecretReference for secret reference validation.
- Implemented Test-ConfigurationDataExpressionParentheses to validate expression syntax.
- Added Test-ConfigurationDataMissingReferenceError to check for missing parameter or variable definitions.
- Updated Invoke-ConfigurationDataExpression to handle new validation logic.
- Revised Readme.md to reflect changes in secret reference handling.

Private/Test-ConfigurationDataExpressionParentheses.ps1

@@ -0,0 +1,39 @@
+function Test-ConfigurationDataExpressionParentheses {
+    [CmdletBinding()]
+    Param(
+        [AllowNull()]
+        [string]
+        $Expression
+    )
+
+    if([string]::IsNullOrWhiteSpace($Expression)){
+        return $true
+    }
+
+    $Depth = 0
+    $InString = $false
+
+    for($Index = 0; $Index -lt $Expression.Length; $Index++){
+        $Character = $Expression[$Index]
+
+        if($Character -eq "'"){
+            $InString = -not $InString
+            continue
+        }
+
+        if($InString){
+            continue
+        }
+
+        if($Character -eq "("){
+            $Depth++
+        }elseif($Character -eq ")"){
+            $Depth--
+            if($Depth -lt 0){
+                return $false
+            }
+        }
+    }
+
+    return $Depth -eq 0 -and -not $InString
+}