[Docs] Document the Compacted format support for Log and PK Tables

[wuchong]

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Description

We’ve now added support for the COMPACTED format for both Log and KV tables (see FLUSS-2218 and PR #2108).

This feature should be documented on the Fluss website to help users understand how and when to use it.

Moreover, when combined with table.changelog.image=WAL, the COMPACTED format enables an efficient, lightweight KV store—ideal for use cases that don’t require full changelog reads or column projections (e.g., future system tables). In such scenarios, there’s no need to look up previous values or deserialize records into an intermediate log format, reducing both latency and CPU overhead.

Willingness to contribute

• I'm willing to submit a PR!

[Priyamanjare54]

I’d like to work on documenting the COMPACTED format. Please let me know if that’s okay.