Proposal: change option to prefer_globus=True and use endpoints stored in config

[nocollier]

At the moment, if a user wants to use Globus transfer to move data, this happens for each call to to_dataset_dict() by passing the globus_endpoint and possibly a globus_path argument(s). This is a lot to type/copy-paste if you always want to use that mode. I think that rather we should let users configure intake-esgf with this information and then let the user signal they prefer_globus=True. We may even consider changing the default to true if an active endpoint is configured.