feat: allow to use hf-models

[cgebbe]

What does this PR do?

Problem: This doesn't currently work, but should in my opinion?

        import transformers
        model = transformers.AutoBackbone.from_pretrained(
            "hf-hub:bioptimus/H-optimus-0",
            use_timm_backbone=True,
            use_pretrained_backbone=True,
        )

Solution approach:

Just remove the two lines which explicitly check whether the string is in timm.list_models(). Alternatively, we could introduce more e.g. backbone_kwargs arguments.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

Who can review?

Models:

• vision models: @amyeroberts, @qubvel