feat(JsonExtensions): create to be able to make fluent Json serilization

EnvelopeGenerator.Application/Common/Notifications/DocSigned/DocSignedNotification.cs

@@ -1,4 +1,5 @@
 using EnvelopeGenerator.Application.Common.Dto.EnvelopeReceiver;
+using EnvelopeGenerator.Application.Common.Extensions;
 using EnvelopeGenerator.Domain.Constants;
 using MediatR;
 using Newtonsoft.Json;
@@ -27,7 +28,7 @@ public record DocSignedNotification(EnvelopeReceiverDto Original) : EnvelopeRece
     /// </summary>
     public string EmailAddress => Receiver?.EmailAddress
         ?? throw new InvalidOperationException($"Receiver is null." +
-            $"DocSignedNotification:\n{JsonConvert.SerializeObject(this, Format.Json.ForDiagnostics)}");
+            $"DocSignedNotification:\n{this.ToJson(Format.Json.ForDiagnostics)}");
 }
 
 /// <summary>