Add perf_infer_gpu_one.mdx italian translation
See issue [https://github.com/huggingface/transformers/issues/17459]
Add Italian translation of perf_infer_gpu_one.mdx and update _toctree.yml.
It's my first pull request, so I hope it's ok
Thanks again for the contribution and congrats on your first PR @davidegazze  🔥 ! Feel free to close the issue if all of the relevant pieces of work have been merged in. 