Missing pyopenjtalk Dependency in ESPnet2 TTS Colab Notebook (Breaks Japanese Synthesis)

Describe the Bug: The ESPnet2 TTS Google Colab notebook does not ensure that pyopenjtalk is installed before running Japanese synthesis, leading to errors when using Japanese TTS models.

When attempting to generate Japanese speech, users may encounter the following error:

ImportError: No module named 'pyopenjtalk'

This issue prevents first-time users from successfully running Japanese synthesis unless they manually install pyopenjtalk.

Basic environments:

• OS information: Google Colab (latest)
• Python version: 3.11 (Google Colab default)
• ESPnet version: Latest version from Colab install
• PyTorch version: 2.1.0 (Google Colab default)

To Reproduce Steps to reproduce the behavior:

1. Open the ESPnet2 TTS Colab Demo.
2. Select a Japanese TTS model for synthesis.
3. Run all steps up to the Synthesis section.
4. If pyopenjtalk is missing, the error appears.

Proposed Fix:

• Add the following before the synthesis step:

  !pip install -q pyopenjtalk

• Should I submit a PR for this fix?