[kotlin-client][jackson] Add missing @JsonEnumDefaultValue annotation to top-level enums

[ken-tunc]

Support for unknown default enum values was added in #17404, but this works for only inner enums in data classes.
This PR fixes to work for top-level enums as well.

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[4brunu]

Thanks for the pull request

[wing328]

@ken-tunc thanks again for the PR

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