Add parameter `preserve_index` to `from_pandas`
> 

I did `make style` and it affected over 500 files

```
All done! ✨ 🍰 ✨
575 files reformatted, 372 files left unchanged.
isort tests src benchmarks datasets/**/*.py metri
```

(result)
![image](https://user-images.githubusercontent.com/20703486/149166681-2f9d1bc4-116a-4f53-ad42-e54e3b8bd605.png)
 Nvm I was using wrong black version
Added optional parameter, so that user can get rid of useless index preserving. [Issue](https://github.com/huggingface/datasets/issues/3563)