Add bash script arguments

[glenn-jocher]

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhanced COCO dataset download script with optional arguments for selective downloading.

📊 Key Changes

• Added optional arguments to specify which parts of the COCO dataset to download (--train, --val, --test, --segments).
• Segregated download and extraction logic for different dataset parts based on the provided arguments.
• Changed the mode of the get_coco128.sh script to be executable.

🎯 Purpose & Impact

• Customizability: Users can now tailor dataset downloading to their specific needs, saving bandwidth and storage.
• Efficiency: The script only processes selected dataset components, making it faster for users who do not require the entire dataset.
• Usability Improvement: This change can enhance the user experience, especially for those with limited resources or specific dataset requirements.