RestClusterClient always leaks flink-rest-client-jobgraphs* directories

After FLINK-32226, a temporary directory(named flink-rest-client-jobgraphs*) is created when creating a new RestClusterClient, but this directory will never be cleaned up.

This will result in a lot of flink-rest-client-jobgraphs* directories under /tmp, especially when using CollectDynamicSink/CollectResultFetcher, which may cause the inode to be used up.