Use parquet export if possible
The idea is to make this code work for datasets with scripts if they have a Parquet export

```python
ds = load_dataset("squad", trust_remote_code=False)
```

And more generally, it means we use the Parquet export whenever it's possible (it's safer and faster than dataset scripts).

I also added a `config.USE_PARQUET_EXPORT` variable to use in the datasets-server parquet conversion job

- [x] Needs https://github.com/huggingface/datasets/pull/6429 to be merged first

cc @severo I use the /parquet and /info endpoints from datasets-server