`animated: true` on shapes to make it blink

https://github.com/terrastruct/d2/issues/1461

It can blink like this, to call attention to an object

https://github.com/terrastruct/d2/assets/3120367/3e70ae0f-b597-4480-8fcb-92c3b1aa62c2

