Allow to read metadata for Canal-json format

In FLIP-107, we support read meta from CDC format Debezium, Canal-json is also

another widely used CDC format , we need to support read metadata too.

The requirement comes from user-zh mail list, the user want to read meta information(database table name) from Canal-json.

[1] http://apache-flink.147419.n8.nabble.com/canal-json-tt8939.html