support coco-wholebody visualization in pose_tracker python demo

[RunningLeon]

Motivation

support coco-wholebody visualization in pose_tracker python demo

Modification

Update demo/python/pose_tracker.py to support coco-whole-body visualization

BC-breaking (Optional)

None

Use cases (Optional)

for mmpose model on coco wholebody like configs/wholebody_2d_keypoint/rtmpose/coco-wholebody/rtmpose-m_8xb64-270e_coco-wholebody-256x192.py

python demo/python/pose_tracker.py \
  cpu \
  /path/to/rtmdet_skd_model \
  /path/to/rtmpose_skd_model \  
  /path/to/test_video \
 --skeleton coco_wholebody

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit tests to ensure the correctness.
3. If the modification has a dependency on downstream projects of a newer version, this PR should be tested with all supported versions of downstream projects.
4. The documentation has been modified accordingly, like docstring or example tutorials.