IterableDataset.add_column is unable to accept another IterableDataset as a parameter.
Hi! You can use `concatenate_datasets([ids1, ids2], axis=1)` to do this.
### Describe the bug

`IterableDataset.add_column` occurs an exception when passing another `IterableDataset` as a parameter.
The method seems to accept only eager evaluated values.

https://github.com/huggingface/datasets/blob/35b789e8f6826b6b5a6b48fcc2416c890a1f326a/src/datasets/iterable_dataset.py#L1388-L1391


I wrote codes below to make it.
```py
def add_column(dataset: IterableDataset, name: str, add_dataset: IterableDataset, key: str) -> IterableDataset:
    iter_add_dataset = iter(add_dataset)

    def add_column_fn(example):
        if name in example:
            raise ValueError(f"Error when adding {name}: column {name} is already in the dataset.")
        return {name: next(iter_add_dataset)[key]}

    return dataset.map(add_column_fn)
```

Is there other way to do it? Or is it intended?

### Steps to reproduce the bug

Thie codes below occurs `NotImplementedError`
```py
from datasets import IterableDataset


def gen(num):
    yield {f"col{num}": 1}
    yield {f"col{num}": 2}
    yield {f"col{num}": 3}


ids1 = IterableDataset.from_generator(gen, gen_kwargs={"num": 1})
ids2 = IterableDataset.from_generator(gen, gen_kwargs={"num": 2})
new_ids = ids1.add_column("new_col", ids1)

for row in new_ids:
    print(row)
```

### Expected behavior

`IterableDataset.add_column` is able to task `IterableDataset` and lazy evaluated values as a parameter since IterableDataset is lazy evalued.

### Environment info
- `datasets` version: 2.8.0
- Platform: Linux-3.10.0-1160.36.2.el7.x86_64-x86_64-with-glibc2.17
- Python version: 3.9.7
- PyArrow version: 11.0.0
- Pandas version: 1.5.3
