Port Variational Inference with Adversarial Learning (VITS) to NeMo TTS
# Overview

This change adds [Variational Inference with adversarial learning (VITS)](https://github.com/jaywalnut310/vits) to the collection of TTS models.

VITS uses the `monotonic_align` module, which requires Cython to be installed prior to building (i.e. run `pip install cython` before running `./reinstall.sh`).

# Tasks

- [x] Fix errors in audio and spectrogram dimensions
- [ ] Fix logging for validation loss
- [ ] Verify training performance
- [ ] Verify quality of TTS output
- [ ] Refactor code and cleanup to be more consistent with other models