fix: nested SpEL record when switching Kafka sink raw editor mode

[qoomak]

Summary

• Fixes switching between structured form and raw editor mode in Kafka sink node
• Dynamic → raw editor: groups dotted param names (combinedState.key, combinedState.tool_record) into proper nested SpEL structure instead of flat dotted keys — flat keys are invalid SpEL and caused type mismatch / validation errors
• Raw editor → dynamic: handles both old flat format and new nested Value expression when distributing back to individual params; normalizes indentation of embedded SpEL records

Test plan

• Open a Kafka Avro sink with dotted params (e.g. combinedState.key, combinedState.tool_record)
• Toggle Raw editor ON — Value expression should be nested: { combinedState: { key: ..., tool_record: {...} }, modelOutput: { value: ... } }
• Toggle Raw editor back OFF — individual params should be restored with correct expressions and clean 2-space indentation
• Verify no validation errors ("only string keys supported") on the Value expression in raw editor mode

[github-actions]

🔴 Cypress snapshot PR created: #9243
Merge it into your branch to update snapshots.
⚠️ Be careful! Snapshot changes are not necessarily the cause of the error. Check the logs.

[qoomak]

Zastąpiony przez #9261

[qoomak]

Superseded by #9261