Refactored CreateDocStatusCommand to remove inheritance from ModifyDocStatusCommandBase and define its own properties. Added EnvelopeId, ReceiverId, and Value properties. Removed the AddedWhen property. The class now directly implements IRequest<DocumentStatus>.
Implement IRequest for CreateDocStatusCommand and add CreateDocStatusCommandHandler to enable MediatR request handling. Add necessary using directives and support repository injection in the handler.
