Notify pending code reviews against non-dev branches about cherry-pick mode

As we switch to cherry-pick mode, pending changes that are still targeting non-dev branches should most probably be targeting dev instead, with a Pick-to: footer added. Owners of these changes should be made aware of this by adding a sanity-bot review, and should have to explicitly override the sanity bot in order to continue with a review against a non-dev branch.

The list of changes in Qt repositories is probably this:
https://codereview.qt-project.org/q/status:open+repos:qt+branch:%255E5.*
 
This requires a one-off process that
 

• adds a -1 sanity bot review
• adds a review message coming from the "Qt Cherry-pick bot" guiding people to the right options (move change and add Pick-to: footer; or abandon change)