Background
When deploying features to a new wiki, the Growth team first deploys it in a shadow/dark mode, meaning the features are not available to newcomers. In the current state of config, it is necessary to override both wgWelcomeSurveyExperimentalGroups (to not show welcome survey to anyone) and wgGEHomepageNewAccountEnablePercentage (to control all other features).
It is easy to make mistakes, forgetting one of those variables.
Proposed solution
Let's mask this with wmgGEFeaturesMayBeAvailableToNewcomers, which will set both variables to the intended values. If we need to change only one of those variables, we can do it easily by changing just one of them.