Support retrieve_online_documents with embedding function

[HaoXuAI]

We can pass an optional embedding function to retrieve_online_documents to embed data first then retrieve top k documents.

E.g,

    def retrieve_online_documents(
        self,
        feature: str,
        embedding: func,
        query: Union[str, List[float]],
        top_k: int,
        distance_metric: Optional[str] = None,
    ) -> OnlineResponse:
      if query is string and embedding:
             embedded_query = embedding(query)
      return retrieve_online_documents(..., embedded_quer)