[gauri-i]

Documents Postgres preserve_toast_values, introduced in olake#1264.

• Updates the UI/CLI docs and shared source.json example
• Explains supported Iceberg pos/dv CDC modes & limitations
• Advises against changing the setting for existing sources or jobs
• Adds troubleshooting fixes: Preserve TOAST Values or REPLICA IDENTITY FULL

Both MDX files compile. Merge after olake#1264 ships.

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✅ gauri-i
❌ Gauri

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[gauri-i]

Closing this PR in favor of #597, which contains the same changes in a single commit.