Add trust_remote_code argument
Draft about adding `trust_remote_code` to `load_dataset`.

```python
ds = load_dataset(..., trust_remote_code=True)  # run remote code (current default)
```

It would default to `True` (current behavior) and in the next major release it will prompt the user to check the code before running it (we'll communicate on this before doing it of course).

```python
# in the future
ds = load_dataset(...)  # prompt the user to check the code before running it (future default)
ds = load_dataset(..., trust_remote_code=True)  # run remote code
ds = load_dataset(..., trust_remote_code=False)  # disallow remote code
```

Related to https://github.com/huggingface/datasets/issues/6400

Will do a separate PR to use the parquet export when possible