Multi-controlnet batching for `StableDiffusionXLControlNetInpaintPipeline`

[kdubovikov]

Is your feature request related to a problem? Please describe. Currently, batching is not supported when we are conditioning the SDXL pipeline on multiple controlnets: https://github.com/huggingface/diffusers/blob/28f9d84549c0b1d24ef00d69a4c723f3a11cffb6/src/diffusers/pipelines/controlnet/pipeline_controlnet_inpaint_sd_xl.py#L771

Describe the solution you'd like. We can pass a list of lists of images for batch inference.

Describe alternatives you've considered. One-by-one processing, which results in very low GPU utilization.

There was a similar PR raised for the StableDiffusionControlNetPipeline https://github.com/huggingface/diffusers/pull/6334