Switch to JS bundling
Currently, the toastui (WYSIWYG editor) JS and CSS are simply downloaded and included from the assets folder, not via npm. I tried to do it using yarn, as we discussed in the meeting, (see cf105b08 and 32a34455 (on another branch)), but I ran into issues with dependencies - the editor has dependencies which also need to be included (which themselves have even more dependencies, and so on...). With the tool we currently use to manage javascript files (Sprockets) it doesn't seem to be possible to automatically resolve and include the dependencies too. To do that, we would need to switch to using something more advanced like Webpack, perhaps Rails' WebPacker (which, however, will no longer receive anything other than security updates as of Rails 7).