Add is_colab() function

[glenn-jocher]

This PR should allow YouTube inference in Colab environments which were crashing due to cv2.imshow().

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Enhancement of the environment detection capabilities in the Ultralytics YOLOv5 utility functions.

📊 Key Changes

• Renamed the isdocker() function to is_docker() to follow the Python naming conventions.
• Added a new function is_colab() to detect if the code is running within a Google Colab environment.
• Updated check_git_status() and check_imshow() functions to incorporate the new is_docker() name.
• Extended check_imshow() to disable image displays in Google Colab environments in addition to Docker.

🎯 Purpose & Impact

• 🎨 Improved code readability and consistency with the renaming of isdocker to is_docker.
• 🧪 Enhanced environment checks help users avoid running image display functions in unsupported environments like Docker and Google Colab, avoiding potential errors and confusion.
• 🔄 General maintenance and verifications are more robust, reducing potential issues for developers working in different environments.