Feature request: hx-init attribute or simpler equivalent

Thank you for providing a refreshing way to create for the web.

I find myself hooking into hyperscript and javascript whenever I need to do some initialisation work on an htmx component.

Hyperscript:

```hyperscript
init log 'init'
```

HTMX JS API:
```javascript
htmx.onLoad(el, () => {
if (el == htmx.find('#my-comp')) {
console.log('init', el)
}
})
```

I imagine `hx-on` could also be used, although I haven't tested it):

```html