Added XLM onnx config
Author: nandwalritik
Pull request: yes

# What does this PR do?

<!--
Congratulations! You've made it this far! You're not quite done yet though.

Once merged, your PR is going to appear in the release notes with the title you set, so make sure it's a great title that fully reflects the extent of your awesome contribution.

Then, please replace this with a description of the change and which issue is fixed (if applicable). Please also include relevant motivation and context. List any dependencies (if any) that are required for this change.

Once you're done, someone will review your PR shortly (see the section "Who can review?" below to tag some potential reviewers). They may suggest changes to make the code even better. If no one reviewed your PR after a week has passed, don't hesitate to post a new comment @-mentioning the same persons---sometimes notifications get lost.
-->

<!-- Remove if not applicable -->

Added XLM OnnxConfig to make this model available for conversion.

@ChainYo 
## Before submitting
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/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.
https://github.com/huggingface/transformers/issues/16308
- [x] 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?

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.

<!-- Your PR will be replied to more quickly if you can figure out the right person to tag with @

 If you know how to use git blame, that is the easiest way, otherwise, here is a rough guide of **who to tag**.
 Please tag fewer than 3 people.

Models:

- albert, bert, xlm: @LysandreJik
- blenderbot, bart, marian, pegasus, encoderdecoder,  t5: @patrickvonplaten, @patil-suraj
- longformer, reformer, transfoxl, xlnet: @patrickvonplaten
- fsmt: @stas00
- funnel: @sgugger
- gpt2: @patrickvonplaten, @LysandreJik
- rag: @patrickvonplaten, @lhoestq
- tensorflow: @LysandreJik

Library:

- benchmarks: @patrickvonplaten
- deepspeed: @stas00
- ray/raytune: @richardliaw, @amogkam
- text generation: @patrickvonplaten
- tokenizers: @n1t0, @LysandreJik
- trainer: @sgugger
- pipelines: @LysandreJik

Documentation: @sgugger

HF projects:

- datasets: [different repo](https://github.com/huggingface/datasets)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Examples:

- maintained examples (not research project or legacy): @sgugger, @patil-suraj
- research_projects/bert-loses-patience: @JetRunner
- research_projects/distillation: @VictorSanh

 -->


Comments:
_The documentation is not available anymore as the PR was closed or merged._

Hello thanks for the PR it looks really clean!! 🤗 

If you have time, it could be nice to upload a converted XLM model to `ONNXConfig for all` organisation on Hugging Face's hub.

> Thanks for this clean PR @nandwalritik fire ! Apart from a small comment about the formatting changes, this LGTM :)
> 
> Could you please confirm that the slow tests pass with:
> 
> ```
> RUN_SLOW=1 pytest tests/onnx/test_onnx_v2.py -s -k "xlm"
> ```
@lewtun The test cases are successfully passing on running `RUN_SLOW=1 pytest tests/onnx/test_onnx_v2.py -s -k "xlm"`.

Thanks for checking the tests pass @nandwalritik ! Could you please rebase on `main` to account for a recent refactoring that was done to order the model names in `features.py` alphabetically?

Hey @nandwalritik are you struggling with the commits or rebasing a branch ?

> Hey @nandwalritik are you struggling with the commits or rebasing a branch ?

I just saw that there were merge conflicts, since `main` was updated, so I rebased again. Did I rebased incorrectly?
Steps which I followed to rebase:- 
* Fetch and merge upstream
* git pull origin main
* git checkout featureBranch
* git rebase main
And then I solved the merge conflicts manually wherever were required.

Yes it seems that there is more than your commits attached to this PR

Nice it seems to be better !


Thanks again for your contribution!