Add support of KNN Query list in NativeQuery

The "knn" option can be a KNN Object or a list of KNN Objects. but NativeQuery can only be assigned one KnnQuery.

<img width="494" height="209" alt="Image" src="https://github.com/user-attachments/assets/90410bca-2fb4-416f-95ab-d90bdd852143" />
https://www.elastic.co/docs/api/doc/elasticsearch/v8/operation/operation-search#operation-search-body-application-json-array-2-knn-array-object