add items order

lib/domain/order/entities/add_item_order_request_entity.dart

@@ -0,0 +1,20 @@
+part of '../order.dart';
+
+@freezed
+class AddItemOrderRequest with _$AddItemOrderRequest {
+  const factory AddItemOrderRequest({
+    required String productId,
+    required String productVariantId,
+    required int quantity,
+    required int unitPrice,
+    required String notes,
+  }) = _AddItemOrderRequest;
+
+  factory AddItemOrderRequest.empty() => AddItemOrderRequest(
+    productId: '',
+    productVariantId: '',
+    quantity: 0,
+    unitPrice: 0,
+    notes: '',
+  );
+}