Fix Llava chat template examples
Author: lewtun
Pull request: yes

# What does this PR do?

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This PR fixes a few minor issues in the chat templating examples for `llava` models. In particular, looking at the [inference code](https://github.com/haotian-liu/LLaVA/blob/4e2277a060da264c4f21b364c867cc622c945874/llava/serve/cli.py#L78-L90) from the original Llava repo, one sees that the correct template is:

```
USER: <image>\n<prompt_1> ASSISTANT:<response_1>
USER: <prompt_2> ASSISTANT:<response_2> etc
```

while we had:

```
USER: <image>\n<prompt_1> \nASSISTANT:<response_1>\nUSER: <prompt_2>\nASSISTANT:<response_2> etc
```

I've only fixed the `llava-v1.5` parts of the code, but happy to extend the PR to cover the other models if we agree with the change.

Code to reproduce the expected template from the Llava repo:

```python
# pip install git+https://github.com/haotian-liu/LLaVA.git
>>> from llava.conversation import conv_templates
>>> conv = conv_templates["llava_v1"].copy()
>>> conv.append_message(conv.roles[0], "<image>\nHello")
>>> conv.append_message(conv.roles[1], "How are you?")
>>> conv.append_message(conv.roles[0], "Good")
>>> conv.append_message(conv.roles[1], "Yay")
>>> conv.get_prompt()
"A chat between a curious human and an artificial intelligence assistant. The assistant gives helpful, detailed, and polite answers to the human's questions. USER: <image>\nHello ASSISTANT: How are you?
USER: Good ASSISTANT: Yay
"
```

## Before submitting
- [x] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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- [ ] Did you write any new necessary tests?


## Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

cc @NielsRogge @amyeroberts 

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Models:

- text models: @ArthurZucker and @younesbelkada
- vision models: @amyeroberts
- speech models: @sanchit-gandhi
- graph models: @clefourrier

Library:

- flax: @sanchit-gandhi
- generate: @gante
- pipelines: @Narsil
- tensorflow: @gante and @Rocketknight1
- tokenizers: @ArthurZucker
- trainer: @muellerzr and @pacman100

Integrations:

- deepspeed: HF Trainer/Accelerate: @pacman100
- ray/raytune: @richardliaw, @amogkam
- Big Model Inference: @SunMarc
- quantization (bitsandbytes, autogpt): @SunMarc and @younesbelkada

Documentation: @stevhliu and @MKhalusova

HF projects:

- accelerate: [different repo](https://github.com/huggingface/accelerate)
- datasets: [different repo](https://github.com/huggingface/datasets)
- diffusers: [different repo](https://github.com/huggingface/diffusers)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Maintained examples (not research project or legacy):

- Flax: @sanchit-gandhi
- PyTorch: See Models above and tag the person corresponding to the modality of the example.
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