Need callback for keyboard navigation.

### Feature

#### Need callback for keyboard navigation.

I was using external index buttons to switch between each `slick-items` using `slickGoTo()` on hover of the buttons. Corresponding button get's highlighted. But on keyboard navigation I never used to get any kind of `onKeyboardNav(index)` notification. I tried using `afterChange()` but it will include all changes. Also `afterChange()` will be triggered only after the animation. So smooth animation of the button highlight is not possible.

https://codesandbox.io/p/sandbox/react-slick-playground-forked-5f49h3