Customer can add and remove from cart, and also get their cart data.
POST
/admin/add-product
addProductsHandler
POST
/user/register
registerUserHandler
PATCH
/user/add-product-to-cart/{userId}/{productId}/{quantity}
addProductToCartHandler
PATCH
/user/remove-product-from-cart/{userId}/{productId}
removeProductFromCartHandler
GET
/user/cart-data/{userId}
getUserCartDateHandler
