Example of using the Navigator

[mfulgo]

As referenced in Workiva/built_redux/issues/92, it would be nice to have an easy to find, canonical example of how to use the navigator when working in Flutter with built_redux.

This information could either be included in documentation or incorporated into the example code.

[smiLLe]

what i am doing is to give a callback into my middleware through the payload.

somewhere in my middleware i am doing sth like this:
action.payload.onSuccess();

and i dispatch my actions like this:
actions.foo(Payload(onSuccess: () { if (mounted) { Navigator.of(context).pop(); }));