feat(GlAlert): `role` status based on alert type

We set aria `role="status"` for alert variants that doesn't necessitate
interrupting the user's current activity. Those variants are `info` and
`tip`.

According to MDN, regarding the aria `role="status"`:

  A `status` is a type of live region providing advisory information that
  is not important enough to justify an alert, which would immediately
  interrupt the announcement of a user's current activity. It is often,
  but not necessarily, presented as a status bar.

https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/status_role

Follow-up from these two comments:

- !3045 (comment 1124896838)
- !3045 (comment 1124893205)