ASR evaluator
# What does this PR do ?

A tool to thoroughly evaluate an ASR model.

**Collection**: ASR

# Changelog 
- Simple step to evaluate a model in all three modes currently supported by NeMo: offline, chunked, and offline_by_chunked.
- On-the-fly data augmentation (silence, noise, etc.,) for ASR robustness evaluation.
- Investigate the model's performance by detailed insertion, deletion, and substitution error rates for each and all samples.
- Evaluate models' reliability on different target groups such as gender, and audio length if metadata is presented.

# Usage

```
python asr_evaluator.py \
engine.pretrained_name="stt_en_conformer_transducer_large" \
engine.inference_mode.mode="offline" \
engine.test_ds.augmentor.noise.manifest_path=<manifest file for noise data>
```

# 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)
- [x] Did you write any new necessary tests?
- [x] 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

## Who can review?

Anyone in the community is free to review the PR once the checks have passed. 
[Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md) contains specific people who can review PRs to various areas.

# Additional Information
Note because the PR is getting bigger, on-the-fly augmentation for buffered inference mode would be included in another PR soon. 
