public void modifyPendingRestarts(ApplicationId id, UnaryOperator<PendingRestarts> modification) {
        try (Lock lock = curator.lock(restartsLockPath(id), Duration.ofMinutes(1))) {
            PendingRestarts original = readPendingRestarts(id);
            PendingRestarts modified = modification.apply(original);
            if (original != modified) {
                if (modified.isEmpty())
                    curator.delete(pendingRestartsPath(id));
                else
                    curator.set(pendingRestartsPath(id), PendingRestartsSerializer.toBytes(modified));
            }
        }
    }
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