[SPARK-50967][SS] Document the case where keys part of the initial state df are also emitted as part of the output

[anishshri-db]

What changes were proposed in this pull request?

Document the case where keys part of the initial state df are also emitted as part of the output

Why are the changes needed?

Explain the case where the initial state might generate unexpected output

Does this PR introduce any user-facing change?

No

How was this patch tested?

Docs only change

Was this patch authored or co-authored using generative AI tooling?

No

[anishshri-db]

cc - @HeartSaVioR - PTAL

there are a couple different ways to fix this:

• document the existing behavior as a limitation
• add a new flag and change the behavior if the feature is enabled (which is a moderate'ish change)

Also, with the new transformWithState operator not having this issue - I wonder whether we should just document this case as such

[anishshri-db]

Discussed offline and we will close this in favor of this PR - #49632 Thx