[TTS] Modify codec training tutorial to allow HF download
[🤖]: Hi @rlangman 👋,

We wanted to let you know that a [CICD pipeline](https://github.com/NVIDIA/NeMo/actions/runs/12250787239) for this PR just finished successfully

So it might be time to merge this PR or get some approvals

I'm just a bot so I'll leave it you what to do next.

//cc @pablo-garay @ko3n1g
# What does this PR do ?

Modify the tutorial about training audio codec models so that the user can download and fine tune from a hugging face checkpoint.

**Collection**: [TTS]

# Changelog 
- Change previous logic using `list_available_models` to instead use `from_pretrained()`
- Replace default 16khz audio codec config with `nvidia/audio-codec-22khz
`
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