Create panoptic segmentation task guide

### Feature request We currently already have a semantic segmentation task guide: https://huggingface.co/docs/transformers/tasks/semantic_segmentation. It would be great to create a similar one for panoptic segmentation with models like MaskFormer, Mask2Former and OneFormer. ### Motivation Panoptic segmentation deserves its own task guide as it's different from semantic segmentation. Lots of people have reported issues, including the following: - [ ] computing mAP during MaskFormer training: https://github.com/NielsRogge/Transformers-Tutorials/issues/373 - [ ] evaluation of DETR and friends on a panoptic segmentation dataset: https://github.com/NielsRogge/Transformers-Tutorials/issues/320 - [ ] there was an effort to add the panoptic quality (PQ) metric to Evaluate: https://github.com/huggingface/evaluate/pull/408 - [ ] various people want to use a COCO-formatted dataset for fine-tuning, but there's no guide yet regarding how to do this: https://github.com/NielsRogge/Transformers-Tutorials/issues/296 ### Your contribution Can be based off the notebooks provided here: https://github.com/NielsRogge/Transformers-Tutorials/tree/master/MaskFormer cc @qubvel