Rebuild plugin-lightbox

[Mister-Hope]

Currently the esm and cjs bundle of plugin-lightbox is useless, as I am not finding out any proper situation for them.

The plugin-katex output file is useful, as the esm cjs file probably works in bundler, or even pure node env.

The lightbox plugin could declare lightbox2 lightGallery, photoswipe fancybox as optional peerDeps and import/require them with try catch block in cjs and esm module. Or it should just remove the 2 files.

It's actually better to add snippets about how to use them with artalk in documentation (intead of providing cjs and esm files).