Add ControlNetUnion to AutoPipeline from_pretrained

[hlky]

What does this PR do?

from diffusers import AutoPipelineForText2Image, AutoPipelineForImage2Image, AutoPipelineForInpainting, ControlNetUnionModel

controlnet = ControlNetUnionModel.from_pretrained("OzzyGT/controlnet-union-promax-sdxl-1.0")
pipe_txt2img = AutoPipelineForText2Image.from_pretrained("stabilityai/stable-diffusion-xl-base-1.0", controlnet=controlnet)
print(type(pipe_txt2img))
pipe_img2img = AutoPipelineForImage2Image.from_pretrained("stabilityai/stable-diffusion-xl-base-1.0", controlnet=controlnet)
print(type(pipe_img2img))
pipe_inpainting2img = AutoPipelineForInpainting.from_pretrained("stabilityai/stable-diffusion-xl-base-1.0", controlnet=controlnet)
print(type(pipe_inpainting2img))

from_pipe will be done in a follow-up.

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.

@yiyixuxu @vladmandic

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[yiyixuxu]

thanks @hlky! maybe we can update the docstring example to use this API