[SDXL] Add SDXL image to image support

[JingyaHuang]

• Img2img pipeline
• Inpaint pipeline
• sdxl refiner export support (refiner unet)
• Tests / Examples
• Documentation update

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint.

[dacorvo]

Just one small nit, and a question: how do we identify the changes as compared to the original methods in the pipeline_stable_diffusion_xx files ?

[JingyaHuang]

@dacorvo for your question, do you mean the sd pipelines in optimum compared to those in diffusers or the difference between sd pipelines and sdxl pipelines?

[dacorvo]

@dacorvo for your question, do you mean the sd pipelines in optimum compared to those in diffusers or the difference between sd pipelines and sdxl pipelines?

The difference between optimum and diffusers: I see that you give the link to the original files, but I was wondering if there were some hints in the code too to identify the lines you changed (I probably missed them).

[JingyaHuang]

@dacorvo there is for sd pipelines: https://github.com/huggingface/optimum-neuron/blob/main/optimum/neuron/pipelines/diffusers/pipeline_stable_diffusion_inpaint.py#L374

But I did not add it when working on sdxl...