[Add] ASR+VAD Inference Pipeline
# What does this PR do ?

This PR aims to provide a pipeline for integrating Voice Activity Detection (VAD) results in ASR inference. 

**Collection**: [ASR]

# Changelog 
- Added example folder `examples/asr/asr_vad`
- Added `feature_to_label.py` and `feature_to_label_dataset.py`
- Added `feature_to_text.py` and `feature_to_text_dataset.py`
- Added classes to `collections.py`
- Updated `manifest.py`

# Usage
To run the code with ASR+VAD default settings:

```bash
python speech_to_text_with_vad.py \
    manifest_filepath=/PATH/TO/MANIFEST.json \
    vad_model=vad_multilingual_marblenet \
    asr_model=stt_en_conformer_ctc_large \
    vad_config=../conf/vad/vad_inference_postprocess.yaml
```

To use only ASR and disable VAD, set `vad_model=None` and `use_rttm=False`.

To use only VAD, set `asr_model=None` and specify both `vad_model` and `vad_config`.

To enable profiling, set `profiling=True`, but this will significantly slow down the program.

To use or disable feature masking, set `use_rttm` to `True` or `False`.

To normalize feature before masking, set `normalize=pre_norm`, 
and set `normalize=post_norm` for masking before normalization.

To use a specific value for feature masking, set `feat_mask_val` to the desired value. 
Default is `feat_mask_val=None`, where -16.530 (zero mel-spectralgram value) will be used for `post_norm` and 0 (same as SpectralAugmentation) will be used for `pre_norm`.

See more options in the `InferenceConfig` class.

# 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?
- [ ] 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.


## 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
* Related to # (issue)
