[postgres] Add changelog mode configuration with upsert/retract modes

[fbad]

This PR implements #1241 proposal with generic code but exposing support in configuration just for postgres module.

I am opening the PR to share one possible implementation of my proposal in a clearer way than words, feel free to close it if it is considered not relevant or not useful for the community.

Fixes #1241

Unstable tests failing because of https://github.com/ververica/flink-cdc-connectors/pull/1181

[ruanhang1993]

I also consider if we should use the name ALL to replace RETRACT.

[fbad]

@ruanhang1993 could you have a look at changes?