Add DALI char dataset support to SSL model
# What does this PR do ?

Use DALI pipelines as part of `ssl_models`

**Collection**: ASR

# Changelog 

- Add DALI char dataset support to SSL model
  
**PR Type**:
- New Feature

Tested manually by running 1 validation step on a local dataset.

## 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 #4591 
