Add boost related events

[hotdoy]

Best case would be a series of events like htmx:beforeBoost, htmx:afterBoost but really, a simple htmx:boosted would probably do the trick.

[hotdoy]

I found out what I needed using the event.detail.boosted of a htmx:afterSwap event. A fully fledged event would still be cool, but at least I'm not feeling the dread anymore.