Alert > Add ability in Storybook to test alert events

Problem

No way to test potential alert roles.

Solution

Include a way to test live alert examples in Storybook that can take advantage of ARIA roles. For example, the modal examples are launched from a button. Triggering an alert would allow us to test the ARIA roles for an alert since those are only announced after being added to the DOM after page load.

See https://www.w3.org/WAI/ARIA/apg/patterns/alert/examples/alert/ for an example.