[Dataset] ESC-50

[snkv04]

What does this PR do?

It implements the retrieval script for ESC-50 and tests that script.

Note: In order to use this dataset, you must have torchcodec and ffmpeg installed.

Before submitting

• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines
• Did you write any new necessary tests?

Who can review?

@RandallBalestriero @Leon-Leyang

[Leon-Leyang]

1. Could you add torchcodec and ffmpeg to pyproject.toml so that the CI tests can install them and run.
2. Also could you run pre-commit run --all-files to pass the precommit test.

Thanks!

[snkv04]

@Leon-Leyang I did both of those, but since ffmpeg is not a pip dependency, I added it to testing.yaml instead of pyproject.toml. I'm not 100% sure if the command will work since ffmpeg was already pre-installed on Hydra so I didn't have to use the installation command, so we can see if it works when the workflow runs