Support Expanding ExecutionGraph to StreamGraph in Web UI

Flink Web shows users the ExecutionGraph (i.e., chained operators), but in some cases, we would like to know the structure of the chained operators as well as the necessary metrics such as the inputs and outputs of data, etc.

Thus, we propose to show the stream graphs and some related metrics such as numberRecordInand numberRecordOut on the Flink Web (As shown in the Figure).