Make an advanced section of our Todo app tutorial and add optimistic updates

Wasp 0.6.0.0 introduced support for optimistic updates via the useAction hook (documented here).

We want to include a section on optimistic updates into our tutorial. The current tutorial tries to avoid being too complicated and we'd like to keep it that way. Therefore, it makes sense to add an advanced section at the end that goes through the more complicated start (optimistic updates for now, maybe jobs and other things in the future).