[feat]: Add example with dynamic transitions to `useTransition` documentation

A clear and concise description of what the feature is

I'm considering submitting a PR (wondering if it would be welcome before I put the work in) to add an example to the useTransition documentation that would answer this Stack Overflow question.

It's my question and I seem to have (mostly) solved it myself by tinkering with the example in the docs. Here is my updated Sandbox

Why should this feature be included?

I think including something like this in the main body of the documentation on transitions (not just in the Demos section) could be helpful because:

1. It uses the function options to the from, enter, and leave props. I had trouble figuring out what those actually were for based on the documentation (ie, what happens when you pass a function arg instead of an object), and really just guessed based on what I thought they might do. Maybe I missed something though.
2. It's an example where the transition is dynamic based on application state, which I feel is lacking in the current documentation.
3. I'm not sure if the isAnimating state is a good approach, but maybe we can decide if it is, and give users a place to start if they need to do something similar. I had to do this because if the transition hadn't finished and you clicked a button, it would go to the wrong index.

Please provide an example for how this would work

It could be a new section in the useTransition documentation page that would be interactive.

Start with the useTransition documentation page and the linked CodeSandbox to understand the proposed dynamic transition example. Done means adding an interactive section that explains function options for from, enter, and leave, and demonstrates transitions driven by application state.