Service Portal: Add to cart is a PITA

So it seems the first thing a lot of places have to do when setting up
the service portal is to re-setup two-step-checkout.

I don't like looking it up. Here's the steps I've followed to set it up;

Adding "Add Cart" on the form

1. On your catalog item widget, ctrl + right click the widget and open
   the widget instance options.
2. Check "Show Add Cart Button"

Adding "Cart" on the header

1. From the Service Portal configuration page, select the Portal editor.
2. Goto the SP Header Menu
3. in the Additional options section ensure you have the following content;

{
  "enable_cart": {
    "displayValue": "true",
    "value": "true"
  }
}

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