Add knn and query search field options to ElasticKnnSearch

[jeffvestal]

in the ElasticKnnSearch class added 2 arguments that were not exposed properly

knn_search added:

• vector_query_field: Optional[str] = 'vector' -- vector_query_field: Field name to use in knn search if not default 'vector'

knn_hybrid_search added:

• vector_query_field: Optional[str] = 'vector' -- vector_query_field: Field name to use in knn search if not default 'vector'
• query_field: Optional[str] = 'text' -- query_field: Field name to use in search if not default 'text'

Fixes # https://github.com/hwchase17/langchain/issues/5633

cc: @dev2049 @hwchase17