Motivation: Tasks like T224903: First Selenium automation test for GrowthExperiments extension (Homepage) are currently impossible in our CI setup (see T199939) since our config switches default to having all features (welcome survey, help panel, homepage, etc) off. As noted in T199939#5106064, the alternative would be to make all features in GrowthExperiments available and working by default.
We would then need to revisit the settings in mediawiki-config repo, both for production and beta labs, and ensure that we switch on any features before they are ready. (However IIRC at the moment all features are enabled for all wikis that use GrowthExperiments.)
Going forward, if a wiki wants to use GrowthExperiments but does not want to use e.g. WelcomeSurvey, we need to ensure that our configuration changes the default from true to false.