Set up login button

Set up the log in button and authentication in the sci-react-ui navbar - see docs [here](https://diamondlightsource.github.io/sci-react-ui/?path=/docs/helpers-auth--docs) to start

- When logged in there should be a choice of visits that can be set
- Buttons can be used
- When not logged in we should still be able to see the screens but all the buttons/selections/etc (essentially whatever interacts with blueapi) should be disabled