Thumbnails for Bento Lightbox Gallery

Can we have different images for the thumbnail and for the lightbox view?

Instead of this…

```html

```

… I need something like this:

```html

```

This might be really useful from the perfomance point of view. Including large images into `` is not a good solution, even if we use lazy loading.

Start by locating the bento-lightbox-gallery component and the lightbox handling for images with the lightbox attribute. Check how the current img src is used, then verify that a separate data-lightbox-src value loads only for the lightbox view while the thumbnail keeps its existing source.

Written by the indexing model from the issue text.