Add missing yaml-parse logic

scripts/Update-OvfConfiguration.ps1

@@ -22,7 +22,24 @@ $ConvertFromYamlSplat = @{
     Yaml         = $RawContent
     AllDocuments = $True
 }
-$OVFConfig = ConvertFrom-Yaml @ConvertFromYamlSplat
+$YamlDocuments = ConvertFrom-Yaml @ConvertFromYamlSplat
+
+# Check if the respective .yml file declared substitutions which need to be parsed
+If (($YamlDocuments.Count -gt 1) -and $YamlDocuments[-1].Variables) {
+    ForEach ($Pattern in $YamlDocuments[-1].Variables) {
+        $RawContent = $RawContent -replace "\{\{ ($($Pattern.Name)) \}\}", [string](Invoke-Expression -Command $Pattern.Expression)
+    }
+    # Perform conversion to Yaml again, now with parsed file contents
+    $ConvertFromYamlSplat = @{
+        Yaml         = $RawContent
+        AllDocuments = $True
+    }
+    $YamlDocuments = ConvertFrom-Yaml @ConvertFromYamlSplat
+    $OVFConfig = $YamlDocuments[0..($YamlDocuments.Count - 2)]
+}
+Else {
+    $OVFConfig = $YamlDocuments
+}
 
 $SourceFile = Get-Item -Path $OVFFile
 $GetContentSplat = @{