Move out common backbone config param validation

[amyeroberts]

What does this PR do?

Moves out the repetitive config validation for backbone config params to one place

[HuggingFaceDocBuilderDev]

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[qubvel]

Will the logic change here? In verify_backbone_config_arguments we have

if not use_timm_backbone and use_pretrained_backbone:
        raise ValueError(
            "Loading pretrained backbone weights from the transformers library is not supported yet. `use_timm_backbone` must be set to `True` when `use_pretrained_backbone=True`"
        )

[amyeroberts]

Yes! For DPT this is because it uses a HF backbone by default and we don't support HF pretrained backbones yet. There's a PR to add this here: #31145

[qubvel]

Looks great to me, so many repetitive code removed 🔪