feat(i18n): add Italian translation

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## Brief Information

This pull request is in the type of:

- [ ] bug fixing
- [x] new feature
- [ ] others



### What does this PR do?

Adds Italian (it-IT) language for locale.




### Fixed issues

N.A.


## Details

### Before: What was the problem?

There was no Italian language localization file present.



### After: How is it fixed in this PR?

A localization file for the Italian language has been added to the codebase.



## Misc

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- [ ] The API has been changed (apache/echarts-doc#xxx).
- [ ] This PR depends on ZRender changes (ecomfe/zrender#xxx).

### Related test cases or examples to use the new APIs

N.A.



## Others

### Merging options

- [ ] Please squash the commits into a single one when merging.

### Other information