Consider adding hookable action on guest author removal

[Antonio-Laguna]

Hey here!

While I can hook into delete_term and see whether a coauthor has been deleted, I wouldn't be able to hook into any of the reassign data that is definitely interesting if you're using CoAuthors Plus in unconventional places.

As an example, you could have additional Credits for a Post leveraging ACF and CoAuthors Plus, if you want to re-map that information you're none the wiser at that stage.

Would you consider adding such do_action? I can definitely contribute