Torchaudio installation fix
Signed-off-by: Aleksandr Laptev <alaptev@nvidia.com>

# What does this PR do ?

Torch and torchaudio versions must match. Othervise, there will be no CUDA support for things like RNNT loss.
This PR fixes the issue.
Also, this PR automates picking the latest torchaudio release.

# Changelog 
- The commands in the Dockerfile are replaced with a separate script whick installs and tests torchaudio.

# Before your PR is "Ready for review"
**Pre checks**:
- [ ] 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**:
- [ ] New Feature
- [x] Bugfix
- [ ] Documentation

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


## Who can review?

@titu1994 @okuchaiev 
