Add BLIP
# What does this PR do?

BLIP is a model from salesforce, capable of performing Visual question answering, image captioning and image-text retrieval. This model has been also used in several Stable-diffusion finetuned variants, such as Pokemon stable diffusion or Naruto Stable diffusion to generate text descriptions from images in order to create text-image paired dataset.

Original repo: https://github.com/salesforce/BLIP 

- [x]  add integration tests
- [x] Push weights
- [x] document everything

Users would be able to use Blip for three main usecases:

1- Conditional Generation (Image captioning):
```
from PIL import Image
import requests
from transformers import BlipForConditionalGeneration, BlipProcessor

img_url = 'https://storage.googleapis.com/sfr-vision-language-research/BLIP/demo.jpg' 
image = Image.open(requests.get(img_url, stream=True).raw).convert('RGB')   

model = BlipForConditionalGeneration.from_pretrained("Salesfoce/blip-image-captioning-base")
processor = BlipProcessor.from_pretrained("Salesforce/blip-image-captioning-base")
text = "a picture of" # the prefix is optional

inputs = processor(image, text, return_tensors="pt")
output = model.generate(**inputs)

print(processor.decode(output[0], skip_special_tokens=True))
>>> a picture of a woman and a dog sitting in a beach
```
1- bis  Conditional Generation (Image captioning with no prefix!):
```
from PIL import Image
import requests
from transformers import BlipForConditionalGeneration, BlipProcessor

img_url = 'https://storage.googleapis.com/sfr-vision-language-research/BLIP/demo.jpg' 
image = Image.open(requests.get(img_url, stream=True).raw).convert('RGB')   

model = BlipForConditionalGeneration.from_pretrained("Salesfoce/blip-image-captioning-base")
processor = BlipProcessor.from_pretrained("Salesforce/blip-image-captioning-base")

inputs = processor(image, return_tensors="pt")
output = model.generate(**inputs)

print(processor.decode(output[0], skip_special_tokens=True))
>>> an image of a woman and a dog sitting in a beach
```

2- Visual question answering
```
from PIL import Image
import requests
from transformers import BlipForQuestionAnswering, BlipProcessor

img_url = 'https://storage.googleapis.com/sfr-vision-language-research/BLIP/demo.jpg' 
image = Image.open(requests.get(img_url, stream=True).raw).convert('RGB')   

model = BlipForVisualQuestionAnswering.from_pretrained("Salesforce/blip-vqa-base")
processor = BlipProcessor.from_pretrained("Salesforce/blip-vqa-base")

question = ["How many dogs are in this image?"]
inputs = processor(image, text, return_tensors="pt")

output = model.generate(**inputs)
print(processor.decode(output[0], skip_special_tokens=True))
>>> 1 
```

3- Image text retrieval (score matching)
```
import torch
from PIL import Image
import requests
from transformers import BlipForQuestionAnswering, BlipProcessor

img_url = 'https://storage.googleapis.com/sfr-vision-language-research/BLIP/demo.jpg' 
image = Image.open(requests.get(img_url, stream=True).raw).convert('RGB')   

model = BlipForImageTextRetrieval.from_pretrained("Salesforce/blip-vqa-base")
processor = BlipProcessor.from_pretrained("Salesforce/blip-vqa-base")

question = ["A picture of a woman with a dog sitting in a beach"]
inputs = processor(image, question, return_tensors="pt")

out_itm = model(**inputs, use_itm_head=True)
out = model(**inputs, use_itm_head=False)

print(out) # cosine similarity score
>>> 0.21
print(torch.nn.functional.softmax(out_itm[0], dim=1)[:, 1])
>>> 0.46
```

cc @NielsRogge 

Fixes https://github.com/salesforce/LAVIS/issues/64
_The documentation is not available anymore as the PR was closed or merged._<|||||>The PR is in a good shape! Would love to have a first round of review! 💪 <|||||>Thanks so much @sgugger @NielsRogge for your review, I can confirm the model weights and model cards are all up!<|||||>Thanks very much for the review @NielsRogge !! <|||||>The failing CI test seems to be related to https://github.com/huggingface/transformers/pull/20790 <|||||>Awesome contribution! Thank you @younesbelkada.

Just noticed Salesforce released BLIP2. Not sure how much work it would be to port to huggingface.
https://github.com/salesforce/LAVIS/tree/main/projects/blip2

