[ASR] Added a script for evaluating metrics for audio-to-audio
Added a script for evaluating audio-to-audio metrics for a manifest file (audio_to_audio_eval.py)

Signed-off-by: Ante Jukić <ajukic@nvidia.com>

# What does this PR do ?

This PR adds a script for evaluation of audio-to-audio metrics.
It is similar to `speech_to_text_eval.py`

This scripts depends on the `process_audio.py` script and inherits all its arguments.

**Collection**: ASR

# Changelog 
- Added `audio_to_audio_eval.py`
- Minor change in `proces_audio`
- Added an option to `get_full_path` to specify `data_dir` directly instead of using `dirname(manifest_file)`

# Usage
* You can potentially add a usage example below

## To score a dataset with a manifest file that contains the input audio which needs to be processed and target audio

```
python audio_to_audio_eval.py \
    model_path=null \
    pretrained_model=null \
    dataset_manifest=<Mandatory: path to a dataset manifest file> \
    output_dir=<Optional: Directory where processed audio will be saved> \
    processed_channel_selector=<Optional: list of channels to select from the processed audio file> \
    target_key=<Optional: key for the target audio in the dataset manifest. Default: target_audio_filepath> \
    target_channel_selector=<Optional: list of channels to select from the target audio file> \
    metrics=<Optional: list of metrics to evaluate. Defaults to [sdr,estoi]>
    batch_size=32 \
    amp=True
```

## To score a manifest file which has been previously processed and contains both processed audio and target audio

```
python audio_to_audio_eval.py \
    dataset_manifest=<Mandatory: path to a dataset manifest file> \
    processed_key=<Optional: key for the target audio in the dataset manifest. Default: processed_audio_filepath>
    processed_channel_selector=<Optional: list of channels to select from the processed audio file> \
    target_key=<Optional: key for the target audio in the dataset manifest. Default: target_audio_filepath> \
    target_channel_selector=<Optional: list of channels to select from the target audio file> \
    metrics=<Optional: list of metrics to evaluate. Defaults to [sdr,estoi]>
    batch_size=32 \
    amp=True
```

# 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

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)
