[TTS] Modify codec training tutorial to allow HF download

[rlangman]

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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[github-actions]

[🤖]: Hi @rlangman 👋,

We wanted to let you know that a CICD pipeline 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