Organize EnvelopeReceiverController and add DocumentExecutor

Updated `EnvelopeReceiverController` with new regions for
creating envelopes and managing recipients, improving code
readability. Added service registration for `IDocumentExecutor`
in `DependencyExtensions.cs` to enhance document management.

EnvelopeGenerator.GeneratorAPI/Controllers/EnvelopeReceiverController.cs

@@ -187,8 +187,11 @@ public class EnvelopeReceiverController : ControllerBase
             CancellationToken cancel = default;
             int userId = User.GetId();
 
+            #region Create Envelope
             var envelope = await _envelopeExecutor.CreateEnvelopeAsync(userId, request.Title, request.Message, request.TFAEnabled, cancel);
+            #endregion
 
+            #region Add receivers
             List<EnvelopeReceiver> sentRecipients = new();
             List<ReceiverGetOrCreateCommand> unsentRecipients = new();
 
@@ -205,6 +208,11 @@ public class EnvelopeReceiverController : ControllerBase
             var res = _mapper.Map<CreateEnvelopeReceiverResponse>(envelope);
             res.UnsentRecipients = unsentRecipients;
             res.SentRecipients = _mapper.Map<IEnumerable<ReceiverReadDto>>(sentRecipients);
+            #endregion
+
+            #region Add document
+
+            #endregion
 
             return Ok(res);
         }