Additional Filtering Criteria for stream_events and stream_log

[willychase]

The feature to filter on component name, tag, or type is nice but there are some additional criteria that would make it more useful:

• Filtering on "event", i.e. excluding "on_chat_model_start"
• Filtering fields in the event itself, i.e. 'metadata' or 'tags'

In my use-case Langserve client is not SSR'd and there is additional data sent to the client that, while not sensitive, is unnecessary for rendering of model responses and tool calls. For example, on_chat_model_start exposes the system prompt and the metadata field contains langgraph-specific and model specific specs.

I'm leaning towards creating a custom stream handler on my backend to handle this, but it seems like something that would be much simpler if it were a filter passed from the client.