Support changing role for Modal

`.

## Is your feature request related to a problem?
`role="dialog"` is not best solution for some cases.

## Describe the solution you'd like
There is `alertdialog` role – a special-case dialog role designed specifically for dialogs that divert users' attention to a brief, important message.

## Additional context
https://github.com/acl-services/paprika/pull/320#discussion_r357880537

https://www.w3.org/TR/wai-aria-practices-1.1/examples/dialog-modal/alertdialog.html

` and review how props are passed through to the wrapper element. Then identify any modal-related tests or snapshots to update for role output and add coverage for `alertdialog` support. A completed PR should allow consumers to configure role while preserving the existing default and include updated expectations/tests for both cases.