Feature request or enhancement

Which use case/requirement will be addressed by the proposed feature?

Currently the built-in SMT "io.debezium.transforms.ExtractNewRecordState" provides "payload.after" content as flattened result for other Kafka connect plugins to use.

However, sometimes it is useful to get only changed columns and optionally primary/unique key columns in a flattened record for further data handling.

It might be great if "ExtractNewRecordState" can optionally compare "payload.before" / "payload.after" fields/values and only keeping changed after-state fields to compose the result flattened record.

Implementation ideas (optional)

Such feature may be implemented by providing the following properties for "ExtractNewRecordState".

• "drop.unchanged.fields" (boolean) : to keep only changed fields in the resulting flattened record
• "null.unchanged.fields" (boolean) : (optional) provides JSON NULL value for all unchanged fields in the resulting flattened record
• "include.primary.keys" (boolean) : to optionally keep primary/unique key fields in the resulting record no matter the previous setting is present or not.