Refactor config loading to async MediatR query in job

Switched FinalizeDocumentJob to use MediatR for async config retrieval, replacing direct model access. Updated _config type to ConfigDto?, injected IMediator, and removed obsolete DbConfig references. Cleaned up ExecuteAsync method for improved clarity and decoupling.

EnvelopeGenerator.ServiceHost/Jobs/State.cs

@@ -9,6 +9,5 @@ public class State
     public int UserId { get; set; }
     public FormUser? User { get; set; }
     public Config? Config { get; set; }
-    public DbConfig? DbConfig { get; set; }
     public MSSQLServer? Database { get; set; }
 }