Italian translation perf_infer_cpu
## What does this PR do?

Italian translation of doc related to the preprocessing of :hugs: Transformers.
* updated _toctree.yml
* added perf_infer_cpu.mdx

## Before submitting
- [X] 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?
- [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.
- [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).

See issue: [[#17459](https://www.linkedin.com/feed/hashtag/?keywords=%2317459)](https://github.com/huggingface/transformers/issues/17459)


@sgugger, @stevhliu, @MKhalusova and @omarespejel 
_The documentation is not available anymore as the PR was closed or merged._