[Vision Transformers] examples and pretraining
# 🚀 Feature request

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Example scripts for fine-tuning and pretraining for clip and Beit models

## Motivation

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At the moment I am training ViT and DeiT for several tasks and thought it would be interesting to compare with clip or from scratch pretrained beit model in self supervised way.
I saw there are already examples for training clip using transformers and flax, not sure if there is an specific reason why it's not already in this repo.

## Your contribution

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If there is someone out who could give me advice, I would be interested adding the Beit pretraining script for pytorch. Longtime I definitely want to add comparisons for several tasks between ViT and from scratch trained BeiT especially for low resource tasks to the hub
This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

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