Enable PyTorch nightly build CI
# What does this PR do?

- Make necessary changes to build `huggingface/transformers-pytorch-nightly-gpu`
- Update `self-nightly-scheduled.yml` to run PyTorch nightly build CI (almost a copy from scheduled CI)

[A run](https://github.com/huggingface/transformers/actions/runs/2347272872) here.

<img width="280" alt="Screenshot 2022-05-18 200718" src="https://user-images.githubusercontent.com/2521628/169114866-cba45123-e388-401d-ab1e-89d04b94b0e9.png">


**Some issue**

The job `run_tests_torch_cuda_extensions_gpu` job couldn't use the image
`huggingface/transformers-pytorch-nightly-gpu`.

In scheduled CI, that job uses `huggingface/transformers-pytorch-deepspeed-latest-gpu`. But so far I haven't do an equivalence to that image for nightly PyTorch.

Would like to hear @LysandreJik regarding this part. Maybe update `transformers-pytorch-deepspeed-latest-gpu/Dockerfile` to have an argument, or just a new Docker file (probably easier)
_The documentation is not available anymore as the PR was closed or merged._