Introduce ndjson writer
This MR is next step to our initiative to introduce ndjson as a way to process import/export(&2734)
We introduced straming_serializer
in #208803 (closed)
This MR:
- implements a NdjsonWriter that writes ndjson using StreamingSerializer.
- it will be based on a feature flag that can switch between fat or ndjson.
Edited by 🤖 GitLab Bot 🤖