remove campaign publishing, allow per-changeset publishing only
Created by: sqs
This is a step toward implementing RFC 157 that I prototyped as I was making storybooks for the new flow (which I'll use to create mocks/screenshots for @eseliger).
Feel free to disregard this PR if it's not helpful. It is just an intermediate step (and if we don't finish other parts of RFC 157 before branch cut, we should revert this PR).