Layoutlmv2 tesseractconfig
# What does this PR do?

Giving user option to set config parameter used by Tesseract when performing feature extraction. Eg. to change psm levels while performing transcription by passing in '--psm 10' to config parameter while invoking image_to_data

It is shown that changing the psm values greatly influences the end result of LayoutLMV2/XLM/V3, and the specific psm value is different depending on the document formatting. Refer : [PSM](https://github.com/tesseract-ocr/tesseract/issues/434)

```python
pytesseract.image_to_data(image, lang=lang, output_type="dict", config="--psm 10") 
``` 

Users can now set the tesseract config parameter during Processor initialization, like so:
```python
# LayoutLMV2
processor = LayoutLMv2Processor.from_pretrained("microsoft/layoutlmv2-base-uncased", ocr_lang="eng", tesseract_config="--psm 5")

# LayoutLMV3
processor = AutoProcessor.from_pretrained("microsoft/layoutlmv3-base", ocr_lang="eng", tesseract_config="--psm 5")
```


## Before submitting
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      Pull Request section?
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      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [❌] Did you write any new necessary tests?
_The documentation is not available anymore as the PR was closed or merged._<|||||>@NielsRogge kindly review. Thanks!<|||||>> LGTM! Could you add it to LayoutLMv3's feature extractor as well?

Sounds good! I'll ping you when it's done. Do I need to do anything to merge this to huggingface:main? You'll trigger the merge is that right?<|||||>>You'll trigger the merge is that right?

Yes, indeed.<|||||>Hi @kelvinAI, could you add it to LayoutLMv3 as well in this PR?

Thanks!<|||||>> Hi @kelvinAI, could you add it to LayoutLMv3 as well in this PR?
> 
> Thanks!

Done! @NielsRogge <|||||>@NielsRogge pls review.
Thanks!<|||||>Hi @kelvinAI, could you apply the suggestions such that I can merge your PR?

Thanks! <|||||>@NielsRogge done! :) 