We would like to test the new header feature (currently living in MobileFrontend's `branding` branch) before deploying to all wikis.
 Ensure T155754 (promotion) has happened
 Ensure T156796 has happened and results are positive.
 Ensure T157476 (logo changes) has happened
 Enable the search icon/branding in the new header to all users on X wikipedia on DATE using the config flag added by T156423
 Create a task to remind us to conclude the test in 2 weeks time and how to continue rolling out.