[Feature Request]: Create a merge-on-read Iceberg sink

[ahmedabu98]

What would you like to happen?

We have an append-only IcebergIO sink.

This is a request to extend the Iceberg sink so that it can receive CDC (insert, update, delete) records from an upstream source and apply them to an Iceberg table.

Issue Priority

Priority: 2 (default / most feature requests should be filed as P2)

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[ahmedabu98]

Full change: #39978

Will break it up into separate PRs