Fix bug for VITS resuming training

[lmxue]

✨ Description

• Fix the bug for VITS resuming training
• Add support for VITS resuming training and fine-tuning.
• Have tested on VITS, including training from scratch, resuming training and fine-tuning, and VALL-E, including stage 1 training and stage 2 training.

🚧 Related Issues

Issue #94

👨‍💻 Changes Proposed

• Add a user-friendly interface in egs/tts/VITS/run.sh to use the arguments related to resuming or fine-tuning VITS model.
• Add support in models/tts/base/tts_trainer.py for fine-tuning VITS model.
• Add usage instructions in egs/tts/VITS/README.md about training VITS from scratch, resuming, or finetuning.

🧑‍🤝‍🧑 Who Can Review?

@viewfinder-annn @RMSnow @VocodexElysium

🛠 TODO

No TODO.

✅ Checklist

• Code has been reviewed
• Code complies with the project's code standards and best practices
• Code has passed all tests
• Code does not affect the normal use of existing features
• Code has been commented properly
• Documentation has been updated (if applicable)
• Demo/checkpoint has been attached (if applicable)

[RMSnow]

LGTM