[TRANSFORM/REST] Handle mismatched column names in the requests

[osery]

Currently, if the input request contains columns that do not match the columns expected by the pipeline, these are silently ignored and the input has NaNs instead. This leads to rather cryptic behavior in real life cases where the input request contains a typo or a lower/upper case differences in the column names.

It would be safer to return error on these requests to make the discrepancy obvious and let the caller decide if an empty value should be used instead or not (= fail fast).