Add Consignment to Checkout

Adds a new consignment to a checkout. Please note that this API endpoint is not concurrent safe, meaning multiple simultaneous requests could result in unexpected and inconsistent results. For more information about working with consignments, see [Checkout consignment](/docs/storefront/cart-checkout/guide/consignments). Though the only required `address` properties to create a consignment are `email` and `country_code`, to successfully [create an order](/docs/rest-management/checkouts/c...