magento-test/app/code/Magento/MediaGalleryRenditions/etc/config.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Store:etc/config.xsd">
    <default>
        <system>
            <media_gallery_renditions>
                <enabled>1</enabled>
                <width>1000</width>
                <height>1000</height>
            </media_gallery_renditions>
            <media_storage_configuration>
                <allowed_resources>
                    <renditions_folder>.renditions</renditions_folder>
                </allowed_resources>
            </media_storage_configuration>
        </system>
    </default>
</config>