Add AmbigQA dataset
# AmbigQA: Answering Ambiguous Open-domain Questions Dataset
Adding the [AmbigQA](https://nlp.cs.washington.edu/ambigqa/) dataset as part of the sprint 🎉 (from Open dataset list for Dataset sprint)

Added both the light and full versions (as seen on the dataset homepage)
The json format changes based on the value of one 'type' field, so I set the unavailable field to an empty list. This is explained in the README -> Data Fields

```py
train_light_dataset = load_dataset('./datasets/ambig_qa',"light",split="train")
val_light_dataset = load_dataset('./datasets/ambig_qa',"light",split="validation")
train_full_dataset = load_dataset('./datasets/ambig_qa',"full",split="train")
val_full_dataset = load_dataset('./datasets/ambig_qa',"full",split="validation")


for example in train_light_dataset:
    for i,t in enumerate(example['annotations']['type']):
        if t =='singleAnswer':
            # use the example['annotations']['answer'][i]
            # example['annotations']['qaPairs'][i] - > is []
            print(example['annotations']['answer'][i])
        else:
            # use the example['annotations']['qaPairs'][i]
            # example['annotations']['answer'][i] - > is []
            print(example['annotations']['qaPairs'][i])

```

- [x] All tests passed
- [x] Added dummy data
- [x] Added data card (as much as I could)
