Return custom metadata from /app/invoke, /app/stream endpoints

[Chengdyc]

Hi, is there a way to return custom metadata from /app/invoke or /app/stream endpoints? currently Langserve only returns the 'run_id' in the metadata dict (invoke) or metadata event (stream) endpoints, optionally the langsmith feedback token could also be returned. but we'd like to return additional custom metadata, e.g. the session-id. Is that supported ? thanks!