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/Dto/EnvelopeHistory/EnvelopeHistoryDto.cs

@@ -1,6 +1,6 @@
 using DigitalData.UserManager.Application.DTOs.User;
 using EnvelopeGenerator.Application.Dto.Receiver;
-using EnvelopeGenerator.Domain;
+using EnvelopeGenerator.Domain.Constants;
 
 namespace EnvelopeGenerator.Application.Dto.EnvelopeHistory;
 
@@ -27,16 +27,16 @@ public record EnvelopeHistoryDto
     /// <summary>
     /// Include code of the envelope at this history point.
     /// </summary>
-    public Constants.EnvelopeStatus Status { get; set; }
+    public EnvelopeStatus Status { get; set; }
 
     /// <summary>
     /// Type of reference for this history entry.
     /// </summary>
-    public Constants.ReferenceType ReferenceType => ((int)Status).ToString().FirstOrDefault() switch
+    public ReferenceType ReferenceType => ((int)Status).ToString().FirstOrDefault() switch
     {
-        '1' => Constants.ReferenceType.Sender,
-        '2' => Constants.ReferenceType.Receiver,
-        _ => Constants.ReferenceType.System,
+        '1' => ReferenceType.Sender,
+        '2' => ReferenceType.Receiver,
+        _ => ReferenceType.System,
     };
 
     /// <summary>