chore: add more parametrization to ingestion test (#2086)
- allow the overwrite destination to be set to the `OUTPUT_ROOT` instead
of default to script dir.
## test
run
```bash
OVERWRITE_FIXTURES=true OUTPUT_ROOT=/tmp ./test_unstructured_ingest/src/s3.sh
```
with this change we should find new files generated under
`/tmp/expected-structured-output/s3`.
Without this change there will be no such new files.
