Add ESC-10 / 50 / US dataset

🚀 Feature

The ESC-10/50 dataset is widely used and no yet available in torchaudio.datasets.
More Information

Motivation

• This dataset is often used as a reference in the same way as its computer vision equivalent: CIFAR or MNIST
• It can be useful for tutorial purposes.
• Its 'US' variant makes it suitable for semi-supervised, self-supervised, and unsupervised learning.
• The ESC-50 and ESC-10 are rather small and may be useful to perform experiments quickly.

Pitch

I am currently using this dataset in my research and I tend to follow the PyTorch way to implement datasets. Therefore, it is almost ready to be submitted here.

• The structure is similar to the already available datasets.
• Downloading the dataset is possible.

I should be able to deliver the code for the end of the week.

Start by reading torchaudio.datasets and the existing dataset implementations, since the issue says this dataset should follow their structure. Verify how downloading is handled, then determine the expected support for ESC-10, ESC-50, and the US variant; done means the datasets are available through torchaudio.datasets and can be downloaded.