[contribution] init script to support Gallery Block

I’m just contributing code that works (for me) with the native Gallery block and this plugin:

document.addEventListener("DOMContentLoaded", function() {
    // Select all divs with an ID starting with "gallery-"
    document.querySelectorAll('.wp-block-gallery').forEach(function(gallery) {
        // For each gallery item within this gallery div
        gallery.querySelectorAll('.wp-block-image').forEach(function(item) {
            // Retrieve the text inside the figcaption element (if exists)
            const caption = item.querySelector('figcaption');
            const captext = caption ? caption.textContent : '';
            // Add the data-sub-html attribute to the corresponding <a> element
            const link = item.querySelector('a');
            if (link) {
                link.setAttribute('data-sub-html', captext);
            }
        });

        // Use className property of <figure> gallery element as ID because it is unique
        const id = gallery.className;

        // Do something with each selected div
        lightGallery(gallery, {
            plugins: [lgFullscreen, lgMediumZoom, lgVideo, lgZoom, lgPager],
            selector: 'a',
            galleryId: id,
        });
    });
});