Re-adding BasketQueryService

src/ApplicationCore/Interfaces/IBasketQueryService.cs

@@ -0,0 +1,12 @@
+using System.Threading.Tasks;
+
+namespace Microsoft.eShopWeb.ApplicationCore.Interfaces;
+
+/// <summary>
+/// Specific query used to fetch count without running in memory
+/// </summary>
+public interface IBasketQueryService
+{
+    Task<int> CountTotalBasketItems(string username);
+}
+