Add BEiTv3
### Model description

Microsoft just open-sourced BEiTv3: https://github.com/microsoft/unilm/tree/master/beit3

This is a very powerful vision-language model that can be used as backbone for a variety of downstream tasks, from image classification to VQA to object detection.

Time to add it to HF Transformers! :)

### Open source status

- [X] The model implementation is available
- [X] The model weights are available

### Provide useful links for the implementation

https://github.com/microsoft/unilm/tree/master/beit3
I will start working on adding the model !<|||||>If required I can help as well<|||||>hello, I want to test the zero shot Image text retrieval of the model on some images and texts, can you help me ?
