[BUG] Default model id not working for nested field

[yuye-aws]

What is the bug?

Here is the discussion from the forum: https://forum.opensearch.org/t/set-up-default-model-id-for-neural-query-enricher-with-nested-knn-field/19217

How can one reproduce the bug?

Follow steps in: https://forum.opensearch.org/t/set-up-default-model-id-for-neural-query-enricher-with-nested-knn-field/19217

What is the expected behavior?

We need to support default model id for nested field.

What is your host/environment?

Operating system, version.

Do you have any screenshots?

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Do you have any additional context?

Add any other context about the problem.