Rename Logger.Warn to Logger.LogWarning throughout codebase

Replaces all usages of Logger.Warn with Logger.LogWarning for consistency with .NET logging conventions. Updates the Logger class method name and all related calls, with no changes to logic or parameters.

EnvelopeGenerator.ServiceHost/Jobs/FinalizeDocument/PDFBurner.cs

@@ -149,8 +149,8 @@ public class PDFBurner : BaseClass
             }
             catch (Exception ex)
             {
-                Logger.Warn("Error in AddInstantJSONAnnotationToPDF - oJson: ");
-                Logger.Warn(json);
+                Logger.LogWarning("Error in AddInstantJSONAnnotationToPDF - oJson: ");
+                Logger.LogWarning(json);
                 throw new BurnAnnotationException("Adding Annotation failed", ex);
             }
         }