fix(cdc): fix some ssl mode issue

[wcy-fdu]

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What's changed and what's your intention?

PgSslMode::prefer means establishing an encrypted connection if the server supports it, and fall back to an unencrypted connection if an encrypted connection cannot be established, and it is also a recommended practice.
I think it is safe to set it to prefer at least for user-defined disable and prefer.

Checklist

• I have written necessary rustdoc comments.
• I have added necessary unit tests and integration tests.
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Release note

[wcy-fdu]

I think in lakekeeper services, should also set to prefer. WDYT @chenzl25

[chenzl25]

I think in lakekeeper services, should also set to prefer. WDYT @chenzl25

Sure. I think you can change it in this PR directly.