code: public function addItem($cartId, Product $product, $quantity = 1, array $options = [], array $extras = [], $note = null)
      {
          $cart = $this->getCartById($cartId);
  
          $cart->addItem($product, $quantity, $options, $extras, $note);
  
          $this->saveCart($cart);
      }
docs: @param int     $cartId
  @param Product $product
  @param int     $quantity
  @param array   $options array( optionSetId => optionId, ... )
  @param array   $extras array( extraSetId_extraId, ... )
  @param string  $note
  
  @throws CartNotFoundException