Modified to be able to use HFTransformers NLP in Japanese

[harada4atsushi]

Proposed changes:

• Issue: HFTransformersNLP dose not work with pretrained Japanese BERT models #5744
• Fixed to use BertJapaneseTokenizer instead of BertTokenizer when Japanese model_weights is specified.

Status (please check what you already did):

• added some tests for the functionality
• updated the documentation
• updated the changelog (please check changelog for instructions)
• reformat files using black (please check Readme for instructions)

[CLAassistant]

All committers have signed the CLA.

[sara-tagger]

Thanks for opening a draft pull request 🚀If you have any questions, you can direct them to @tabergma ✨

[dakshvar22]

@harada4atsushi Thanks for suggesting a fix. For better maintainability of the code, I would suggest creating a custom component at this point for yourself. The component can inherit from HFTransformersNLP component and just override _load_model method to load the corresponding japanese specific tokenizer and model.
Adding a conditional construct in Rasa just for one language could get out of hand very soon IMO. There might be a better approach of solving this by using AutoTokenizers but that would also require more amount of refactoring on the internal implementation of HFTransformersNLP

[harada4atsushi]

@dakshvar22 Thank you for your comment and suggenstion. Certainly that's right, I attempt to implement custom component.