Overriding definition of BIDS-defined TSV columns with custom JSON entries

[sappelhoff]

In other news: What happens if a dataset curator uses a pre-defined column (like sample) in their dataset, but supply a definition for sample in their JSON file that completely diverges from the BIDS definition? I don't think we have a section for this case in the specification, but it feels like we should. And I believe this should be NOT RECOMMENDED, however if it's being done, we could state that the "user override" is be authoritative.

Originally posted by @sappelhoff in https://github.com/bids-standard/bids-specification/issues/1441#issuecomment-1475951326