Refactor EnvelopeStatus usage and streamline code

- Added `EnvelopeGenerator.Domain.Constants` in multiple files, replacing `Domain.Constants.EnvelopeStatus` with `EnvelopeStatus` for improved readability.
- Modified `CreateEnvelopeCommandHandler.cs` to directly use `request.UserId`, eliminating unnecessary local variable assignment.
- Identified potential duplication in query logic within `ReceiverAlreadySignedQuery.cs`.
- Updated `IEnvelopeService`, `EnvelopeReceiverService`, and `EnvelopeService` to ensure consistent usage of the simplified `EnvelopeStatus`.
- Overall, these changes enhance code maintainability and clarity.

EnvelopeGenerator.Application/EnvelopeReceivers/Queries/ReceiverAlreadySignedQuery.cs

@@ -1,11 +1,10 @@
 using DigitalData.Core.Abstraction.Application.Repository;
-using DigitalData.Core.Exceptions;
 using EnvelopeGenerator.Application.Model;
-using EnvelopeGenerator.Domain;
 using EnvelopeGenerator.Domain.Entities;
 using EnvelopeGenerator.Application.Extensions;
 using MediatR;
 using Microsoft.EntityFrameworkCore;
+using EnvelopeGenerator.Domain.Constants;
 
 namespace EnvelopeGenerator.Application.EnvelopeReceivers.Queries;
 
@@ -70,9 +69,9 @@ public class ReceiverAlreadySignedQueryHandler : IRequestHandler<ReceiverAlready
     public async Task<bool> Handle(ReceiverAlreadySignedQuery request, CancellationToken cancel = default)
     {
         return await _repo.Read()
-            .Where(er => er.Envelope.Uuid == request.Envelope.Uuid)
-            .Where(er => er.Receiver.Signature == request.Receiver.Signature)
-            .Where(er => er.Envelope.History.Any(hist => hist.Status == EnvelopeStatus.DocumentSigned))
+            .Where(er => er.Envelope!.Uuid == request.Envelope.Uuid)
+            .Where(er => er.Receiver!.Signature == request.Receiver.Signature)
+            .Where(er => er.Envelope!.History.Any(hist => hist.Status == EnvelopeStatus.DocumentSigned))
             .AnyAsync(cancel);
     }
 }