Support for Feature Flags

Similar to what is/will be possible on Android, we would benefit from the ability to toggle feature flags from some kind of developer screen/mode within the app itself rather than only having build time flags. Additionally, if we build this with the potential to toggle flags remotely (possibly via PostHog), it would help for rolling out new features across all clients simultaneously as well as the disabling any features at the last minute if issues are discovered just before launch.