feat(PDFBurnerParams): add DefaultIndexOfAnnot and GetAnnotationIndex

- add `DefaultIndexOfAnnot` property to provide a fallback index for annotations
 - add `GetAnnotationIndex(string name)` method to safely retrieve an annotation index, returning default if not found

EnvelopeGenerator.Application/Common/Configurations/PDFBurnerParams.cs

@@ -57,4 +57,16 @@ public class PDFBurnerParams
         { "city", 2 },
         { "date", 3 }
     };
+
+    /// <summary>
+    /// 
+    /// </summary>
+    public int DefaultIndexOfAnnot { get; set; } = 0;
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="name"></param>
+    /// <returns></returns>
+    public int GetAnnotationIndex(string name) => IndexOfAnnot.TryGetValue(name, out var value) ? value : DefaultIndexOfAnnot;
 }

EnvelopeGenerator.Application/Pdf/BurnPdfCommand.cs

@@ -256,7 +256,7 @@ public class BurnPdfCommandHandler : IRequestHandler<BurnPdfCommand>
 
     private void AddFormFieldValue(Annotation pAnnotation, FormFieldValue formFieldValue)
     {
-        var ffIndex = _pdfBurnerParams.IndexOfAnnot[pAnnotation.EgName];
+        var ffIndex = _pdfBurnerParams.GetAnnotationIndex(pAnnotation.EgName);
   
         // Convert pixels to Inches
         var oBounds = pAnnotation.Bbox?.Select(ToInches).ToList();