Add required dependency 'spacy[ja]' to DockerFile to support `enable_text_splitting=True`

[riven8192]

long texts on the TTS endpoint yield:
ImportError: enable_text_splitting=True requires Spacy: pip install spacy[ja]

Given that enable_text_splitting is True by default, please ensure this dependency is added to the Dockerfile
RUN pip install "spacy[ja]"

[matatonic]

Thanks for the report, but this software is no longer maintained and I consider it obsolete. I will leave this comment for anyone else who this might help. The README has some possible alternatives.