We would like to test the new header feature (currently living in MobileFrontend's `branding` branch) before deploying to all wikis.
[x] Ensure T155754 (promotion) has happened
 Ensure T156796 has happened and results are positive.
[x] Ensure T157476 (logo changes) have happened.
 Enable the search icon/branding in the new header to all users on Catalan and Italian wikipedia on Monday ~~20th~~~ (TBC) using the config flag added by T156423. Ensure T156423 has rolled out to these wikis before deploying.
 Create a task to remind us to conclude the test in 2 weeks time and how to continue rolling out.