Add VLM support

[merveenoyan]

This PR adds VLM support (closing other one for the sake of collaboration) @aymeric-roucher

• This PR at the creation is probably broken (since you wanted to see it) primarily because as of now when you're writing memory you adopt chat templates like following:

messages = [
  {"role": "user", "content": "I'm doing great. How can I help you today?"},
]

whereas with VLMs we do like following so I modified a bit.

messages = [
  {"role": "user", "content": [{"type": "text", "text": "I'm doing great. How can I help you today?"},
{"type":"image"}
]

but you access content and modify it here and there so it is broken: (fixing)

• Secondly I need to check if I'm adding images necessarily only once because it will break the inference if we pass one image more than once, I add it in multiple steps, so I will see.

Will open to review once I fix these.

[merveenoyan]

@aymeric-roucher we can keep images in action step with a separate key. normally models do not produce images, so if we put images with "images" key it will break chat template. if we keep images for the sake of keeping images, we can keep it under a different key like "observation_images" (just like how we do in the function).

[merveenoyan]

we need to unify the image handling for both OpenAI & transformers I think, I saw you overwrote templates which could break transformers. will handle tomorrow

[merveenoyan]

@aymeric-roucher can I write the tests now? will there be changes to API?