Iterating over values of a column in the IterableDataset
### Feature request

I would like to be able to iterate (and re-iterate if needed) over a column of an `IterableDataset` instance. The following example shows the supposed API:
```
def gen():
    yield {"text": "Good", "label": 0}
    yield {"text": "Bad", "label": 1}

ds = IterableDataset.from_generator(gen)
texts = ds["text"]

for v in texts:
    print(v)  # Prints "Good" and "Bad"

for v in texts:
    print(v)  # Prints "Good" and "Bad" again
```

### Motivation

In the real world problems, huge NNs like Transformer are not always the best option, so there is a need to conduct experiments with different methods. While 🤗Datasets is perfectly adapted to 🤗Transformers, it may be inconvenient when being used with other libraries. The ability to retrieve a particular column is the case (e.g., gensim's FastText [requires](https://radimrehurek.com/gensim/models/fasttext.html#gensim.models.fasttext.FastText.train) only lists of strings, not dictionaries).
While there are ways to achieve the desired functionality, they are not good ([forum](https://discuss.huggingface.co/t/how-to-iterate-over-values-of-a-column-in-the-iterabledataset/135649)). It would be great if there was a built-in solution.

### Your contribution

Theoretically, I can submit a PR, but I have very little knowledge of the internal structure of 🤗Datasets, so some help may be needed.
Moreover, I can only work on weekends, since I have a full-time job. However, the feature does not seem to be popular, so there is no need to implement it as fast as possible.