Feature: Allow setting the activeIndex via props

[pke]

It would be nice to be able to set the activeIndex to some specific (clamped) index for advanced usage.

I am currently using an effect to goToSlide but this does not update the activeDots and next and done buttons.

const { id } = props
const ref = useRef<AppIntroSlider>(null)
useEffect(() => {
  ref.current && ref.current.goToSlide(id)
}, [id, ref]