The RemoteConfig instance.
The ConfigUpdateObserver to be notified of config updates.
An Unsubscribe function to remove the listener.
If a connection to the Remote Config backend is not already open, calling this method will open it. Multiple listeners can be added by calling this method again, but subsequent calls re-use the same connection to the backend.
The list of updated keys passed to the callback will include all keys not currently active, and the config update process fetches the new config but does not automatically activate it for you. Typically you will activate the config in your callback to use the new values.
Starts listening for real-time config updates from the Remote Config backend and automatically fetches updates from the Remote Config backend when they are available.