[FEAT] Add Custom Whisper Models Addon

[Mad-Jam]

Is this a new feature request?

• I have searched the existing issues

Wanted change

Add support for custom Whisper models (e.g., kb-whisper) via an environment variable like WHISPER_MODEL. This would allow users to specify and use non-English or specialized models.

Reason for change

Non-English languages often need larger or language-specific models for better accuracy.

Proposed code change

No response

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[Mad-Jam]

Tried to add 'KBLab/kb-whisper-medium' to environment 'WHISPER_MODEL' (docker, CPU only). It just worked.
A comment in README.MD that other whisper models from Hugging Face can work.