Group-residual vector quantizer
# What does this PR do ?

This PR adds group-residual vector quantizer as in http://arxiv.org/abs/2305.02765

**Collection**: TTS

# Changelog 
- Added group-RVQ
- Added unit tests for RVQ

# Usage
To use, add the following in the config file

```yaml
  vector_quantizer:
    _target_: nemo.collections.tts.modules.encodec_modules.GroupResidualVectorQuantizer
    num_codebooks: 4 # total number of codebooks
    num_groups: 2 # number of groups
    codebook_dim: 128 # dimension of the audio encoder output
```

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**Pre checks**:
- [x] Make sure you read and followed [Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md)
- [x] 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

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


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# Additional Information
* Related to # (issue)
