Context

Weaviate's implementation is almost identical to ours. We already had an issue making metadata json-serializable with ObjectIds. I came across the following function in their code for datetimes in [Weviate's vectorstore.py](https://github.com/langchain-ai/langchain/blob/master/libs/community/langchain_community/vectorstores/weaviate.py)

```

def _json_serializable(value: Any) -> Any:
    if isinstance(value, datetime.datetime):
        return value.isoformat()
    return value

```

Definition of done

Add this to our make_serializable function.

What must be done to consider the task complete?

Pitfalls

What should the implementer watch out for? What are the risks?