[SFT VLM] Added support for Molmo models via standalone script sft_vlm_molmo

[sergiopaniego]

What does this PR do?

Fixes #2136.

This PR presents a standalone version for adding support to Molmo models. It may benefit from a generalization to be compatible with sft_vlm.py

This notebook has a reproducible version, both running the script or using code directly.

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• Did you write any new necessary tests?

Who can review?

@lewtun @edbeeching @qgallouedec

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