[Audio datasets] Adapting all audio datasets
This PR adds the new `Audio(...)` features - see: https://github.com/huggingface/datasets/pull/2324 to the most important audio datasets:

- Librispeech
- Timit
- Common Voice
- AMI
- ... (others I'm forgetting now)

The PR is curently blocked because the following leads to a problem:

```python
from datasets import load_dataset

# load first time works
ds = load_dataset("patrickvonplaten/librispeech_asr_dummy", "clean") 

# load from cache breaks
ds = load_dataset("patrickvonplaten/librispeech_asr_dummy", "clean") 
```

As soon as it's unblocked, I'll adapt the other audio datasets as well. 