add FAN model (vision)
### Model description

Fully attentional networks (FAN) is a family of general-purpose Vision Transformer backbones that are highly robust to unseen natural corruptions in various visual recognition tasks.

### Open source status

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

### Provide useful links for the implementation

* https://github.com/NVlabs/FAN
* https://arxiv.org/abs/2204.12451
Hi there, I would like to implement this model @NielsRogge <|||||>Hi @NielsRogge.
To my knowledge there would still be two pending tasks
- [X] Update README.md to include FAN model
- [ ] Migrate Files, weights to NVIDA organization space
Please let me know what additional tasks you think might be pending