feat(extensions): created extensions project.

- Moved encoding extensions from application to extensions project to increase the abstraction

EnvelopeGenerator.Web/Controllers/DocumentController.cs

@@ -4,6 +4,7 @@ using EnvelopeGenerator.Web.Services;
 using EnvelopeGenerator.Application.Contracts;
 using Microsoft.AspNetCore.Authorization;
 using EnvelopeGenerator.Application;
+using EnvelopeGenerator.Extensions;
 
 namespace EnvelopeGenerator.Web.Controllers
 {