Add Italian translation for `add_new_model.mdx`
# What does this PR do?

Italian translation of `add_new_model.mdx` 
Related to issue: #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
- [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.
@mfumanelli  @nickprock 
Hi @Steboss89 , is a very long document well done! At the moment I read until the line 339.
It's ok but:
row 75: esssere --> essere
row 91: Similmente al modello --> Analogamente al modello

And the phrase "I files del modello devono esssere il più self-contained possibile cosicché quando leggi il codice di uno specifico modello, idealmente, 
avresti da vedere solo il corrispettivo file `modeling_....py`." is unclear.<|||||>Hey @Steboss89! Thank you for your translation! And thank you, @nickprock for your kind review 🙏. 

@Steboss89, additionally to what @nickprock mentioned, to pass the quality tests, make sure you run `make quality` on the main page of your directory. [Here are the instructions](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md).<|||||>It's actually `make style` ;-) <|||||>Hi @Steboss89.

row 426: arhcitettura --> architettura 
row 446: che `init()` di tutte le componenti funziona correttamente. --> che `init()` di tutte le componenti funzioni correttamente.
row 454: Di solito é abbastanza fare una copia di uno script gia esistente e adattarlo al vostro caso. --> Di solito basta fare una copia di uno script gia esistente e adattarlo al vostro caso.
row 628: dobbiamo assicurarci che il vostro lavoro sia correttamente testato --> bisogna assicurarsi che il vostro lavoro sia correttamente testato
row 648: `BrandNewBertModelTester`/`BrandNewBertModelTest`
row 714: ttuto --> tutto
row 726: A volte capita che mancano delle informazioni --> A volte capita che manchino delle informazioni<|||||>Sorry for not coming back with corrections and tests earlier
I'll get through the quality checks as well as the corrections suggested 
Thanks a million @nickprock @sgugger and @omarespejel  
<|||||>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.<|||||>Hey @nickprock  sorry again for such a long delay. Here is the corrected version of the documentation.

@sgugger and @omarespejel  I can see from the quality check that these files: 
```
['src/transformers/benchmark/benchmark_utils.py', 'src/transformers/testing_utils.py', 'src/transformers/trainer_utils.py', 'src/transformers/modelcard.py', 'src/transformers/utils/notebook.py', 'src/transformers/models/auto/auto_factory.py', 'src/transformers/models/transfo_xl/modeling_transfo_xl.py', 'src/transformers/models/xlm/tokenization_xlm.py', 'src/transformers/models/tapex/tokenization_tapex.py', 'src/transformers/models/perceiver/modeling_perceiver.py', 'src/transformers/models/flaubert/tokenization_flaubert.py', 'src/transformers/models/fsmt/tokenization_fsmt.py', 'src/transformers/generation_utils.py', 'src/transformers/generation_flax_utils.py', 'src/transformers/generation_tf_utils.py', 'src/transformers/trainer_pt_utils.py']
```
needs restyle. How can I fix this? Thanks <|||||>Your PR is a bit old now, so you will first need to rebase your branch on main (or start a fresh PR, whatever is easiest).<|||||>@sgugger  Thanks very much 
I'll rebase my branch with current main :) <|||||>_The documentation is not available anymore as the PR was closed or merged._