Refactor EnvelopeDto property for receiver handling

Replaced the `Receivers` property with `EnvelopeReceivers` in the `EnvelopeDto` class to improve clarity and better align with the updated data model. The new property uses `IEnumerable<EnvelopeReceiverDto>?` instead of `IEnumerable<ReceiverDto>?`.

EnvelopeGenerator.Application/Common/Dto/EnvelopeDto.cs

@@ -133,5 +133,5 @@ public record EnvelopeDto : IEnvelope
     /// <summary>
     /// 
     /// </summary>
-    public IEnumerable<ReceiverDto>? Receivers { get; set; }
+    public IEnumerable<EnvelopeReceiverDto>? EnvelopeReceivers { get; set; }
 }