[docs] improve autocomplete docs for filter callback second parameter

[DRiFTy17]

The current docs for the autocomplete in Storybook do not properly convey the filter callback usage around the second value parameter. We need to make this more clear and obvious for our consumers.

The value parameter is passed by the autocomplete when it doesn't have an option loaded that matches the value currently set, so it will "ask" the developer via the filter callback using this parameter so that they can go fetch that single option label to display.