Visual Attention Network (VAN)
# What does this PR do?
This PR adds [Visual Attention Network](https://arxiv.org/pdf/2202.09741.pdf). 

Currently, the model can be used as follows

```python
import requests
from io import BytesIO
res = requests.get('https://github.com/huggingface/transformers/blob/master/tests/fixtures/tests_samples/COCO/000000039769.png?raw=true')
image = Image.open(BytesIO(res.content))

feature_extractor = AutoFeatureExtractor.from_pretrained("zuppif/van-base")
model = VanForImageClassification.from_pretrained("zuppif/van-base").eval()

inputs = feature_extractor(image, return_tensors="pt")
outputs = model(**inputs)
print(model.config.id2label[torch.argmax(outputs.logits).item()])
# tabby, tabby cat
```

## TODO
- [x] modeling
- [x] weights
- [x] doc
- [x] tests

_The documentation is not available anymore as the PR was closed or merged._<|||||>Thanks for the reviews. I've resolved all the comments that can be resolved and asked the authors if we can create an organization for them in the hub.