Port Riva's mel cepstral distortion w/ dynamic time warping notebook
# What does this PR do ?

Ports the Riva Mel Cepstral Distortion - Dynamic Time Warping notebook (nvidia-riva/tutorials#96) to NeMo.

HTML version here for ease of viewing:
https://drive.google.com/file/d/1E7bk95HQXZE_LyCfryr1r9LEKPzm8J9D/view?usp=sharing

**Collection**: TTS

# Changelog 
- Minor changes to ensure the notebook runs both locally and in Colab (tarred the example data, changed the way the audio is displayed)
- Additional docstrings and function explanations
- Minor text updates
  
**PR Type**:
- [x] New Feature
- [ ] Bugfix
- [x] Documentation

If you haven't finished some of the above items you can still open "Draft" PR.
