[FEATURE] Add quantity of cart items to Header component

[connoro7]

Feature Request

Add the number of items in a user's cart (show 0 if empty) to the link text for Cart to the JSX return in /frontend/components/Header.js.

[connoro7]

Possible solution:

It should be enough to grab the cart state from Redux;

const cart = useSelector((state) => state.cart)
  const { cartItems } = cart
// cartItems type:array

And add {cartItems.length} to the return.

[connoro7]

Just using {cartItems.length} will return the number of unique items in a user's cart.
For example, if a user has ItemX in their cart, with a quantity of 3, {cartItems.length} will return 1, but expected behavior is to return 3.