save_pretrained crashes when torch_dtype is passed
If you have the following code

```
p = pipeline(... torch_dtype=torch.bfloat16)
p.save_pretrained()
```

you get a crash because `torch.bfloat16` is not json serializable in the `tokenizer.save_pretrained()` method.

This PR fixes this.

@Narsil
@ArthurZucker

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_21986). All of your documentation changes will be reflected on that endpoint.<|||||>My understanding that the following code should work

```
from transformers import pipeline
p = pipeline("some/model", torch_dtype=torch.bfloat16)
``` 

from what I can see the tokenizer kwargs basically start with copy of the model_kwargs? 

https://github.com/huggingface/transformers/blob/main/src/transformers/pipelines/__init__.py#L869<|||||>Indeed, this means that the problem is bigger! Popping the argument is good if we want to keep the pipeline that way, I think we agreed to properly handle the extra tokenizer kwargs @Narsil if you want to take care of it, it will fix this! <|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.<|||||>@ArthurZucker @Narsil What do you want to do here. I think this PR does the right thing at the moment because extra arguments to the pipeline are passed around to the tokenizer and then the tokenizer crashes on save_pretrained. 
I think merging this is strictly better than the current state. Sure the code could be improved internally. Conceptually there should be something that decides which kwargs to the pipeline should be passed to each of the components in the pipeline.<|||||>Hey! Thanks for reporting the bug, I merged something that seemed more aligned with what we want: torch dtype should just not be passed to the tokenizer, so poping it outside