Review huggingface_hub integration

[Wauplin]

TL;DR:

• timm is compatible with huggingface_hub v0.x and v1.x
• bump minimal version (still very lax)
• fix a bug when upload to private repo
• clean some stuff

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At first I just wanted to check that the current implementation was compatible with the upcoming huggingface_hub v1.0 release (see huggingface/huggingface_hub#3340). This is indeed the case (breaking changes should not affect timm). However I took the advantage to update the huggingface_hub integration, and especially:

• use file_exists instead of get_hf_file_metadata + hf_hub_url in order to check if the repo user is uploading to has a README
• bump minimal version to v0.17.0 which has been release in Sept' 2023 and introduced file_exists utility. I don't think this bump is a major problem as it's 2 years old.
• do not recreate repo_id manually using repo_type_and_id_from_hf_id as this is already done by the create_repo return value (since Dec' 2022 so included in v0.17+)
• use HfApi instead of individual methods when uploading a model
  • => allows to set custom user-agent for timm (only done for hf_hub_download so far)
  • => allow to pass token once and for all => previously the get_hf_file_metadata(hf_hub_url(repo_id=repo_id, filename="README.md", revision=revision)) was necessarily failing in case of private repo since token was not forwarded

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[HuggingFaceDocBuilderDev]

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