Branched off discussion in #61825

Add an [ ] Alert me if there's no data checkbox to the alert creation form. If this is checked, the alert should go into a No Data state and fire an action to send a No Data message.

By default, this action should send a message on all of the same channels the user has configured for a regular alert. e.g. if the user is receiving Slack messages and emails when the alert fires, also send the No Data notification over Slack and email