magento-test/app/code/Magento/Quote/Test/Mftf/Metadata/CustomerCartItemMeta.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
 /**
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
-->

<operations xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:mftf:DataGenerator/etc/dataOperation.xsd">

    <operation name="CreateCustomerCartItem" dataType="CustomerCartItem" type="create" auth="adminOauth" url="/V1/carts/{quote_id}/items" method="POST">
        <contentType>application/json</contentType>
        <object key="cartItem" dataType="CustomerCartItem">
            <field key="quote_id" type="string">string</field>
            <field key="sku" type="string">string</field>
            <field key="qty">integer</field>
        </object>
    </operation>
</operations>