Support yolo-seg data process

[wenshinlee]

I exported the Ultralytics YOLO Segmentation 1.0 dataset using CVAT. However, when loading it with Datumaro, it failed to recognize the type of the database. I noticed that the current annotation files support <label_index> <x_center> <y_center> . Can it support instance segmentation tasks?

[wenshinlee]

This is the data format of yolo-seg.