Replace User class with EGUser across the codebase

This commit introduces the new `EGUser` class, which replaces the existing `User` class in multiple files, including `EnvelopeModel.vb`, `State.vb`, and `UserModel.vb`. The `EGUser` class extends `User`, adding new properties while maintaining existing functionality.

Key changes include:
- Updated property types from `User` to `EGUser` in relevant models.
- Method signatures in `UserModel.vb` modified to accept and return `EGUser`.
- Domain entities in `Envelope.cs` and `EnvelopeHistory.cs` now reference `EGUser`.
- Complete removal of the `User.cs` file.
- Added a new package reference for `UserManager.Domain` in the project file.
- Updated `MYUSER` variable in `ModuleSettings.vb` to use `EGUser`.

These changes enhance the user model to better meet application requirements.

EnvelopeGenerator.Domain/Entities/Envelope.cs

@@ -113,7 +113,7 @@ namespace EnvelopeGenerator.Domain.Entities
 
         // TODO: * Check the Form App and remove the default value
         [ForeignKey("UserId")]
-        public User User { get; set; } = new User();
+        public EGUser User { get; set; } = new EGUser();
 
         [ForeignKey("EnvelopeTypeId")]
         public EnvelopeType EnvelopeType { get; set; }