Added italian translation for parallelism.mdx
## What does this PR do?

Italian translation of parallelism.mdx
See issue: https://github.com/huggingface/transformers/issues/17459

## 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.
https://github.com/huggingface/transformers/issues/17459


## 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.
@mfumanelli 


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Models:

- albert, bert, xlm: @LysandreJik
- blenderbot, bart, marian, pegasus, encoderdecoder,  t5: @patrickvonplaten, @patil-suraj
- longformer, reformer, transfoxl, xlnet: @patrickvonplaten
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- rag: @patrickvonplaten, @lhoestq
- tensorflow: @LysandreJik

Library:

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- deepspeed: @stas00
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Documentation: @sgugger

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Examples:

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The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_18301). All of your documentation changes will be reflected on that endpoint.<|||||>Thank you, @Xpiri, for the translation!

@sgugger it seems this doc no longer exists in the current documentation (it used to be in the `how-to-guides` section). What do you think we should do?<|||||>Yes, this document has been split into several pages, performance.mdx and each perf_xxx document. So we should translate those pages and not the document that doesn't exist anymore.<|||||>Well, I guess if the other documents use parts that are identical to this document, perhaps we could just split this file.

@mfumanelli I would also suggest to review the main thread, just to make sure we are not working on an older version of the docs 😄 <|||||>Hey @Xpiri! Sorry for the confusion. 

I have updated issue #17459 with the docs in which `parallelism` was partitioned. Would it be a bad idea to update this PR with this new info? We would completely understand if this is the case.<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.