Retrieves a single purchase order by ID

query {
    purchaseOrder(id: 1) {
        purchase_order_id
        purchase_code
        po_date
        expected_date
        currency
        supplier_id
        supplier_name
        ship_to_name
        ship_to_address
        discount_label
        discount_amount
        tax_label
        tax_amount
        shipping_label
        shipping_amount
        status
        created_at
        updated_at
        items {
            purchase_order_product_id
            product_id
            variant_id
            inventory_item_id
            product_name
            product_sku
            product_supplier_sku
            variant_name
            product_image
            variant_image
            qty_ordered
            qty_received
            cost
            sales_price
        }
    }
}