Migrate detectron2_training.ipynb to use HuggingFace Hub

[mturk24]

Replace S3 URL for labels.pkl with HuggingFace Hub download:

• Add huggingface_hub import to imports cell
• Replace wget S3 command with hf_hub_download() call
• Use Cleanlab/object-detection-tutorial dataset with repo_type="dataset"

This ensures consistency with the main tutorials and eliminates dependency on S3 storage.