Add OvisImagePipeline in AUTO_TEXT2IMAGE_PIPELINES_MAPPING

[alvarobartt]

What does this PR do?

This PR adds the OvisImagePipeline in the AUTO_TEXT2IMAGE_PIPELINES_MAPPING, so that Ovis-Image models e.g. https://huggingface.co/AIDC-AI/Ovis-Image-7B, can be loaded with the AutoPipelineForText2Image as it's currently producing ValueError: AutoPipeline can't find a pipeline linked to OvisImagePipeline for None.

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@yiyixuxu and @asomoza

[HuggingFaceDocBuilderDev]

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[yiyixuxu]

thanks!