Expose record metadata to mongo-cdc

[bobby-richard]

Is your feature request related to a problem? Please describe.
It's possible to capture data from multiple mongo databases and collections with the connector, but there is no way to know which database or collection each record came from.

Describe the solution you'd like
The official flink debezium format provides a way to read debezium metadata fields when creating a table DDL (https://nightlies.apache.org/flink/flink-docs-release-1.13/docs/connectors/table/formats/debezium/#available-metadata). Something similar could be done to expose db and collection from the mongo source connector document.

I'm happy to take a stab at this if someone could point me in the right direction.

[fsk119]

I think you can take a look at the FLIP about the design of the metadadta column. Flink has an good example in the PR[2].

[1] https://cwiki.apache.org/confluence/display/FLINK/FLIP-107%3A+Handling+of+metadata+in+SQL+connectors
[2] apache/flink#13732

[wuchong]

I'm going to support metadata columns for mysql-cdc in the next days, see #249. I think it can be a good example for other connectors.

[leonardBang]

Implemented in 65665eb