We've always taken a pretty hands-off approach, preferring to encourage

conversation over policy. That said, one of the most requested bits of

policy is to make it so users can't mark their own review requests as

"Ship It". This is not only a reasonable policy ask (especially if

people are using approval workflows that can block pushes), but should

probably be the default.
This change implements that. The visibility of the "Ship It" action and

checkbox in the review dialog are now conditional on this flag, and

reviews will refuse to publish (either via the UI or API).
Because a big change like this may be controversial, I've added a toggle

for it in the admin settings, under a new page titled "Review Workflow".

Viewed a review request as both the owner and another user, and saw

  that the visibility of the action and review dialog checkbox was

  correct.
Toggled the setting in the admin and checked again, seeing that I

  could restore previous behavior.
Ran unit tests.