Add feature to disable bert as a switch

[apinge]

As python code snippet in get_text_for_tts_infer

if getattr(hps.data, "disable_bert", False):
        bert = torch.zeros(1024, len(phone))
        ja_bert = torch.zeros(768, len(phone))

Required by the customer

[apinge]

Resolved in https://github.com/apinge/MeloTTS.cpp/commit/6595c43976e18d71e12fdc4dda179b238eaf4658