[docs] Fix image segmentation guide

[stevhliu]

Fixes #30058:

• adds import for Accelerate
• adds code snippet to view image but also keeps viewing the metadata as well since imo its important to see the other fields in there
• reloads the dataset in the Inference section
• adds the ade_palette colormap manually so the code snippet just runs (let me know if there is a better way to import the colormap!)

[HuggingFaceDocBuilderDev]

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[amyeroberts]

Thanks for this update!