[ASR] Add official ASR CTC example to `examples/pytorch/speech-recognition`
This PR adds a generic speech recognition for CTC example. It has been tested for single GPU and distributed training on Common Voice and is being tested on Librispeech currently.

Once `datasets` has https://github.com/huggingface/datasets/pull/2324/files merged and made a new release I will slightly adapt the script to leverage the new audio feature.

A couple of example runs with this script:
- https://huggingface.co/patrickvonplaten/wav2vec2-common_voice-tr-demo
- https://huggingface.co/patrickvonplaten/wav2vec2-common_voice-tr-demo-dist

This example folder should have two additional scripts: 1 for Seq2Seq ASR + 1 for CTC + LM decoding which are left for future work