incrementItemToCart method
This function is used to increment the item quantity into cart
Implementation
incrementItemToCart(int index) {
_cartItemList[index].quantity = ++_cartItemList[index].quantity;
_cartItemList[index].subTotal =
(_cartItemList[index].quantity * _cartItemList[index].unitPrice)
.roundToDouble();
return CartResponseWrapper(true, _successMessage, _cartItemList);
}