Expose the discount class for applied_discounts and discount_allocations on a line item for the Checkout Admin REST API

The 2023-07 API version of the Checkout Admin REST API will expose the discount_class attribute in the line_items[n].applied_discounts and line_items[n].discount_allocations.

The discount_class identifies the type of discount applied to a line_item:

PRODUCT - denotes a Product class discount that applies to specific products only. ORDER - denotes an Order class discount that applies across all line items.

The following example shows the "discount_class": "ORDER" present for the line item when an order class discount was applied to a checkout.

"line_items": [
    {
        "id": "a93dfd7540730e5d9812a92fac5a640e",
        "key": "a93dfd7540730e5d9812a92fac5a640e",
        "product_id": 6,
        "variant_id": 10,
        "sku": "jeans1",
        "vendor": "",
        "title": "Jeans",
        "variant_title": "Black",
        "image_url": "",
        "taxable": true,
        "requires_shipping": true,
        "gift_card": false,
        "price": "50.00",
        "compare_at_price": "30.00",
        "line_price": "50.00",
        "properties": {},
        "quantity": 1,
        "grams": 0,
        "fulfillment_service": "manual",
        "applied_discounts": [],
        "discount_allocations": [
            {
                "id": null,
                "amount": "20.00",
                "description": "ORDER$20",
                "created_at": null,
                "application_type": "discount_code",
                "discount_class": "ORDER"
            }
        ],
        "tax_lines": []
    }
],