feat: add profit and special discount fields to ProductVariant model

- Updated ProductVariant model to include 'profit' and 'special_discount_percent' fields.
- Added corresponding fields in the admin interface for ProductVariant.
- Created migration to add new fields to the database.

feat: implement special discount code functionality in cart

- Added composables for submitting and deleting special discount codes.
- Updated CartSummary and CartItem components to handle special discount codes.
- Enhanced API endpoints to support special discount operations.
- Updated global types to include special discount code details in the cart.

backend/order/urls.py

@@ -8,9 +8,11 @@ urlpatterns = [
     path('cart', CartView.as_view()),
     path('cart/set-address', SetAddressForCartView.as_view()),
     path('cart/discount', ApplyDiscountView.as_view()),
+    path('cart/special-discount', ApplySpecialDiscountView.as_view()),
     path('cart/all', CartItemClear.as_view()),
     path('cart/item/<int:pk>', CartItemViews.as_view(), name='change-item-cart'),
     path('cart/payment', PaymentView.as_view(), name='payment'),
-    path('transaction/<int:tracking_code>', CallbackView.as_view(), name='callback-gateway'),
+    path('transaction/<int:tracking_code>',
+         CallbackView.as_view(), name='callback-gateway'),
     path('<int:pk>', OrderGetView.as_view(), name='order-get'),
 ]