fix: set MODEL_ID in sagemaker-entrypoint script

[xyang16]

What does this PR do?

Currently setting HF_MODEL_ID environment variable does not take effect. It will always use the default bloom model.

So I raise this PR to set MODEL_ID with HF_MODEL_ID in sagemaker-entrypoint script. I have tested it in SageMaker.

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Who can review?

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@OlivierDehaene OR @Narsil

[OlivierDehaene]

Thanks