Add check-group component

[thiagomajesk]

I got the idea from this post in the Fly IO blog: https://fly.io/phoenix-files/making-a-checkboxgroup-input/. From my experience, this is used very very often and it's basically a necessity to have a good abstraction over it.

The implementation from the post is not particularly great because the .input core component is very limited.
We can abstract it and create our own primitive following the respective WAI-ARIA recommendations for this.
BTW, it would go hand-in-hand with the existing idea of implementing a radio-group component like Radix UI: https://www.radix-ui.com/docs/primitives/components/radio-group.