Refactor Dockerfiles to utils/docker

[glenn-jocher]

Also add lighter Dockerfile-cpu for CPU-only environments.

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Improvements to Docker setup for YOLOv5 including organization and CPU-only support 🐳.

📊 Key Changes

• 🚚 Moved .dockerignore and Dockerfile to utils/docker/ directory to improve project organization.
• 🎨 Updated Dockerfile to add an additional font Arial.Unicode.ttf for enhanced text support.
• 🧹 Cleaned up the Dockerfile by removing a redundant environment variable setting.
• 🆕 Added a new Dockerfile-cpu for creating a CPU-only Docker image, which provides an alternative for environments without GPU support.

🎯 Purpose & Impact

• 🗂️ Organizing Docker-related files helps maintain a clean and structured repository.
• ✏️ Adding Unicode font support offers better text rendering, especially for non-Latin characters, which is crucial in a globalized context.
• 🧼 Removing unnecessary code simplifies the Docker image and reduces potential confusion for users customizing their environment.
• 💻 The CPU-only Dockerfile allows users without GPUs to easily deploy YOLOv5, broadening the reach and usability of the software on more devices and platforms.