Document kebab-case event names for hx-on

I just spent quite a bit of time debugging why `hx-on:htmx:afterOnLoad` wasn't firing.

The [docs](https://htmx.org/docs/#hx-on) say it isn't possible to handle this event with `hx:on`:

> Note that HTML attributes are case insensitive. This means that, unfortunately, events that rely on capitalization/ camel casing, cannot be responded to.

And the `debug` extension only displays the camelCase event names.

However, buried deeper in that same paragraph in the docs the very solution to this limitation is provided:

> htmx dispatches all its events in both camelCase and in kebab-case for this very reason.

I eventually figured out that `hx-on:htmx:after-on-load` very much does the trick.

This was much harder to find than it should have been.

Ideally https://htmx.org/events/ should be updated to included all kebab-case events as well. Or event better, it should **only mention the kebab-case event names as those work everywhere**. The camelCase event names can remain supported in the library for backwards compatibility.