feat: add "auto" language for TesseractOcr

[pavel-denisov-fraunhofer]

Add language-agnostic OCR option for TesseractOcr module. It is invoked when the language option is set to ['auto']. For more context, see the discussion: #640

Please let me know what you think.

Checklist:

• Documentation has been updated, if necessary.
• Examples have been added, if necessary.
• Tests have been added, if necessary.

[mergify]

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[nikos-livathinos]

We can merge this PR and implement the optimized version at a follow up PR

[pavel-denisov-fraunhofer]

We can merge this PR and implement the optimized version at a follow up PR

Sorry for the delay! I was going to check it in the next few days, but can make a follow up PR too.

The problem with CI is that the script OCR models are not installed: https://github.com/DS4SD/docling/actions/runs/12806245234/job/35994648426?pr=759#step:8:155

[pavel-denisov-fraunhofer]

Ubuntu package tesseract-ocr-script-latn puts the model to the data directory itself (without script subdirectory): https://packages.ubuntu.com/noble/all/tesseract-ocr-script-latn/filelist

I'm going to add the check if script/ prefix is needed when loading the script model.

[nikos-livathinos]

Looks good to me