Add dota8.yaml and O tests (#7394)

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

ultralytics/cfg/datasets/DOTAv1.yaml

@@ -5,7 +5,7 @@
 # parent
 # ├── ultralytics
 # └── datasets
-#     └── dota2  ← downloads here (2GB)
+#     └── dota1  ← downloads here (2GB)
 
 # Train/val/test sets as 1) dir: path/to/imgs, 2) file: path/to/imgs.txt, or 3) list: [path/to/imgs1, path/to/imgs2, ..]
 path: ../datasets/DOTAv1  # dataset root dir