Install torchaudio as dep for examples

Summary:
This package is required in order to run emformer rnnt models, which is not a required package nor installed package for executorch yet. This diff is to add the required package.

And we are picking up the latest `torchaudio` library, which is  `2.1.0.dev20230810`

Minor notes/comments change.

Reviewed By: kimishpatel

Differential Revision: D48284923

fbshipit-source-id: aa6ef28c700cb20f7bfdbda529a609f92d1b6984