Support huggingface

[not-lain]

this pr will mainly add 3 methods to the uniformer model

• save_pretrained
• push_to_hub
• from_pretrained : initialize and load the model weights

allowing your model to be easily integrated with huggingface using the PyTorchModelHubMixin class, I made this notebook explaining how to use it

Why you should integrate your model with huggingface ?

• easily save, load and push your model
• Keep track on how many times your model has been downloaded by the community.
• Automatic model card generation: the metadata in the card allows you to filter your searches easily to check how many UniFormer models exist on the Hub .
• Recommended: after this pr is merged we can open a pull request on this file to make the "UniFormer" library official on the Hub meaning better discoverability + possibility to add code snippets.

do not hesitate if you have any reviews on the pr or any questions.

Kind regards,
Hafedh Hichri