🚨🚨🚨Change default from `adamw_hf` to `adamw_torch` 🚨🚨🚨
# What does this PR do?

This PR changes the default from `adamw_hf` to `adamw_torch`, as noted in https://github.com/huggingface/transformers/issues/25006 which fixes some breaking issues. Note that https://github.com/huggingface/transformers/issues/22141 still needs to be fulfilled once torch 2.1.0 is released (sometime in the next few months I imagine, as we're on 2.0.1) and swap it to be `ADAMW_TORCH_FUSED`. 

Fixes # (issue)

Solves #25006 

## Maintaining old behavior

To keep the old behavior prior to this change, ensure that you pass `"adamw_hf"` as the `optim` in your `TrainingArguments`


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [ ] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


## Who can review?

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@sgugger @stas00 

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