Move .dockerignore to root

[glenn-jocher]

Resolves #8685

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Relocation of .dockerignore file for better organization.

📊 Key Changes

• Renamed and moved .dockerignore file from utils/docker/ directory to the root directory.

🎯 Purpose & Impact

• Simplifies Docker context by having .dockerignore at project root, which can lead to faster build times.
• Provides a more standard structure that is easier for developers to recognize and use.
• Reduces the risk of accidentally including unnecessary files in Docker builds, making container images more secure and lightweight. 🚀