Refactor enum usage in codebase

Updated references from `Constants` to direct usage of `EnvelopeStatus` and `EmailTemplateType` enums. This change enhances code readability and reduces dependency on the `Constants` class.

Modified properties and parameters across command classes, DTOs, repositories, and services to use the enums directly. Updated `ModifyDocStatusCommandBase`, `EnvelopeHistoryDto`, and `ResetEmailTemplateCommand` for improved clarity.

Consistent updates across multiple files indicate a systematic refactoring aimed at streamlining the codebase and improving maintainability. Comments and documentation have also been revised to reflect these changes.

EnvelopeGenerator.Application/EmailTemplates/Queries/Read/ReadEmailTemplateQueryHandler.cs

@@ -41,7 +41,7 @@ public class ReadEmailTemplateQueryHandler : IRequestHandler<ReadEmailTemplateQu
     {
         var temp = request.Id is int id
             ? await _repository.ReadByIdAsync(id)
-            : request.Type is Constants.EmailTemplateType type
+            : request.Type is EmailTemplateType type
                 ? await _repository.ReadByNameAsync(type)
                 : throw new InvalidOperationException("Either a valid integer ID or a valid EmailTemplateType must be provided in the request.");