Add alpha value in `wtpsplit`

[pavaris-pm]

According to the original paper 'Where's the Point? Self-Supervised Multilingual Punctuation-Agnostic Sentence Segmentation,' we have an option to adjust the paragraph threshold using the paragraph_threshold argument in wtpsplit. This threshold corresponds to the alpha value mentioned in the paper's method section. I already made a PR at #806 include the usage and output example of using that alpha value, with that, we can specify the paragraph threshold for wtpsplit if we want. What do you think ?

[github-actions]

Hello @pavaris-pm, thank you for your interest in our work!

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[wannaphong]

I agree. 👍