To ensure a smoother deployment of the Parsoid support for Kartographer (in particular, allowing a longer testing phase and/or progressive deploy), we want to add a feature flag (set to false by default) for the Parsoid support.
This feature flag must be removed when the Parsoid rollout is complete (and this phab should not be closed before that happens). Note that it is used in tests as well and that it should be cleaned up from there as well.