[Enhancement]: Add option to enable notification email when ActionScheduler past-due queue hits a certain threshold

[cagrimmett]

Describe the solution you'd like

When the ActionScheduler had a backed up past-due queue, there is a notification at the top of wp-admin. That is great, but you have to log in and see it. What would be great is a notification email to the admin once it hits a certain theshold, perhaps one that is user-defined. And a user-defined frequency of hourly/daily/weekly.

Describe alternatives you've considered

This can be added via custom code, but it would be a great product improvement!

Additional context

This came from a client using Woo Subscriptions, because a flood of traffic and a slow webhook endpoint caused the ActionScheduler to back up with over 32K actions over the course of 24 hours.