refactor(Extension): move to Application.Extensions and remove the project.

- update references

EnvelopeGenerator.GeneratorAPI/Controllers/HistoryController.cs

@@ -1,4 +1,4 @@
-using EnvelopeGenerator.Extensions;
+using EnvelopeGenerator.Application.Extensions;
 using MediatR;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;