[Draft] [TTS] Fastpitch restructure
# What does this PR do ?

AudioToCharWithDursF0Dataset class will be deprecated so this PR adds code and config to use old FastPitch checkpoint (checkpoint that was trained using AudioToCharWithDursF0Dataset class which is now deprecated) with new code (TTSDataset) to support inference.

**Collection**: tts.models.fastpitch

# Changelog 
- Adds Warning when using old checkpoint
- Adds config file to be used with old checkpoint

# Usage
* In FastPitchModel.from_pretrained use https://github.com/NVIDIA/NeMo/tree/main/examples/tts/conf/fastpitch_align_old.yaml \
   as config_file to avoid using deprecated AudioToCharWithDursF0Dataset class and run into errors. \

```python
# FastPitchModel.from_pretrained("tts_en_fastpitch", override_config_path="/path/to/fastpitch_align_old.yaml") 
```

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**PR Type**:
- [ ] New Feature
- [ ] Bugfix
- [ ] Documentation

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# Additional Information
* Related to # (issue)
