Enable add_prefix_space on run_ner if necessary
# What does this PR do?

Enable add_prefix_space for a tokenizer on run_ner and run_ner_no_trainer if it needs to be instantiated with.

Fixes #9607


## 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/master/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [x] 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/master/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/master/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


I've tested it:
```
% python -m pytest -n auto --dist=loadfile -s -v ./examples/ 
...
Results (256.02s):
      24 passed
      21 skipped
```

additionally checked style and quality then fixed it up:
```
% make style && make quality && make fixup                       
...
All done! ✨ 🍰 ✨
```

## Who can review?

Examples:

- maintained examples (not research project or legacy): @sgugger, @patil-suraj

Thanks for your PR, but this is too complicated. The examples are just example, and should be modified by users directly for specific use-cases, we can't support everything out of the box.<|||||>@sgugger I agree with you it's somewhat complicated.

So, I've pushed codes that simplified as possible and also support for training roberta.

Actually I've experienced #9607 on training roberta for ner task.
Refering to #9607, only roberta-base and roberta-large have the issue. 
So, it's enough that run_ner supports roberta for now.

If you think it's still too complicated, I will close this pr and just use it for me.<|||||>Thank you for your suggestion!
Let me update the pr.<|||||>I've updated the pr.
@sgugger, please take a look through it.