export to yolov8 format

[huhuang03]

Accoding to https://docs.ultralytics.com/modes/train/#introduction

The yolov8 should have a yaml file, and have trian, validate folder, and in each folder, theres label and imgs folder

[estepnv]

don't forget about keypoints

[ice6]

+1

[ArturVRSampaio]

+1

[siyangbing]

+1

[Sovenok-Hacker]

+1