Release v19.25.2

Fixed

• A quarantined observer now stays quarantined when its grain is deactivated or reactivated, for example after it has been idle or the Kernel restarts. Before, it silently showed as Disconnected. The quarantine ends when an operator clears it or when the observer is subscribed again, and a subscription then retries failed partitions and resumes stopped jobs as for any reconnecting observer. When a quarantine ends lists exactly what subscribes each kind of observer again. (#4426)