DOC: <Issue related to /evaluation/how_to_guides/upload_existing_experiments>

[becaha]

The doc says you should be able to upload an experiment with metadata. The response I get from the upload experiment post request has an object 'extra' in it that has the metadata that I defined in my payload, but no metadata is showing up in the experiment in the LangSmith console. I have put metadata in both experiment_metadata and run_metadata but no metadata shows up. The experiment is uploaded correctly otherwise.