Refactor namespaces to follow new naming convention and add item model classes

Controllers/PetController.cs

@@ -1,8 +1,8 @@
 using Microsoft.AspNetCore.Mvc;
-using pet_companion_api.Models;
-using pet_companion_api.Services;
+using Pet.Companion.Models;
+using Pet.Companion.Services;
 
-namespace pet_companion_api.Controllers
+namespace Pet.Companion.Controllers
 {
     [ApiController]
     [Route("api/v1/[controller]")]