Adding a custom property, modifying the Nav_Waker_Menu_Edit for Wordpress. (Code extract from https://github.com/AlphaGit/alphasmanifesto/blob/master/custom_menu_setup.php)

customNavWalkerMenuEdit.php

<?php
    // modify the displayed dom for editing menu items so that they provide the new value
    add_action( 'wp_edit_nav_menu_walker', 'alphasmanifesto_edit_nav_menu_walker' );
    function alphasmanifesto_edit_nav_menu_walker($walker) {
        return "AlphasManifestoNavMenuEditWalker";
    }
    
    class AlphasManifestoNavMenuEditWalker extends Walker_Nav_Menu  {
        //...
        function start_el(&$output, $item, $depth, $args) {
            //...
            
            // after the last field, before the submitbox code
            ?>
                <p class="field-image-url description description-wide">
                    <label for="edit-menu-item-image-url-<?php echo $item_id; ?>">
                        <?php _e( 'Image URL' ); ?><br />
                        <input type="text" id="edit-menu-item-image-url-<?php echo $item_id ?>" class="widefat code edit-menu-item-image-url" name="menu-item-image-url[<?php echo $item_id; ?>]" value="<?php echo esc_attr($item->image_url); ?>" /?
                    </label>
                </p>
            <?php
            //...
        }
    }