Snake act
# What does this PR do ?

Add snake activation to Audio Codec

**Collection**: TTS/ASR

# Changelog 
- Add Snake Activation to activation file
- Optionally choose between ELU/Snake while building model
- Note: Prior checkpoints don't load as is without modifying variable names 


# Before your PR is "Ready for review"
**Pre checks**:
- [x] Make sure you read and followed [Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md)
- [ ] Did you write any new necessary tests?
- [ ] Did you add or update any necessary documentation?
- [ ] Does the PR affect components that are optional to install? (Ex: Numba, Pynini, Apex etc)
  - [ ] Reviewer: Does the PR have correct import guards for all optional libraries?
  
**PR Type**:
- [x] New Feature
- [ ] Bugfix
- [ ] Documentation
