An Unified Example Format Checker

[innerNULL]

What does this PR do?

In trl/data_utils.py, some List are appeared in variables in different functions (e.g. is_conversational and apply_chat_template), and this may cause some maintaining burdens, and this is are start of checking example format information in an unified approach.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a GitHub issue? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

[qgallouedec]

what is this new arg?

[qgallouedec]

Thanks for your contribution, I'm having trouble understanding the new logic. It seems to allow supported_keys, non_label_keys and label_keys to be set, but the supported keys are still hard-coded in your new function? Also, what do you mean by "label keys"? For example, why shouldn't chosen be one?
Can you provide a little more context on the motivation for this PR and the problem it solves?

[qgallouedec]

Closing as no update from the author, feel free to re-open if needed