public PendingRestarts readPendingRestarts(ApplicationId id) {
        try (Lock lock = curator.lock(restartsLockPath(id), Duration.ofMinutes(1))) {
            return curator.getData(pendingRestartsPath(id))
                          .map(PendingRestartsSerializer::fromBytes)
                          .orElse(PendingRestarts.empty());
        }
    }
List the active applications of a tenant in this config server.

@return a list of {@link ApplicationId}s that are active.
configserver/src/main/java/com/yahoo/vespa/config/server/application/ApplicationCuratorDatabase.java