Return a "Not Implemented" error when `_field` is used in a predicate passed to the delete API

[danxmoran]

Our delete-by-predicate API doesn't support filtering on _field (see #20399). When users try to filter on it now, they get back a successful response code even though no data is deleted. We should directly check for use of _field in predicates and return a "Not Implemented" error so users aren't surprised when their data never gets removed.

[timhallinflux]

Not implemented implies (to some degree) that we are planning on implementing this at some point. I would suggest throwing an error which indicated that delete by _field is not supported.

[e-dard]

I assume the confusion is (to some extent) that the documentation doesn't say you can't provide _field as part of the predicate? https://docs.influxdata.com/influxdb/v2.0/reference/syntax/delete-predicate/

The OSS 2 documentation looks like it's exactly the same as the Cloud documentation where it is currently possible to include the _field key in the predicate to limit deleted data to a single field.

[bo-stud]

Hi, is there anything going to happen soon to resolve this struggle. And is there another way to delete by field. I tried a workaround via a very narrow timeframe but if different fields have the exact same timeframe it is not possible to delete just one of the fields. Any help would be appreciated :)