Update docs for react_router using SSR

[jeremylynch]

The current docs for react-router are outdated and incomplete: https://www.shakacode.com/react-on-rails/docs/javascript/react-router/

It would be great to update the following:

• Update to use React router v7
• Update redux to use configureStore rather than createStore (deprecated)
• Show recommended way of setting up redux store when using react_on_rails

And a full end-to-end example of setting react_router with SSR would be fantastic!