Support `ALTER TABLE x AUTO_INCREMENT = 100`

Support for adjusting the autoincrement counter would be useful in Playground for resetting the default WordPress content.

Right now you may get 3 or 4 or 5 pages by default, depending on a WordPress release and you can't easily create a page and redirect to, say, `/wp-admin/post.php?post=4&action=edit` because the ID won't be reliably 4. Maybe it will be 3, maybe 5, or maybe 6.
