convert(...) changed to save target file alongside the original file

[IlyaOvodov]

Current behaviour when convert(...) function saves converted file always as 'converted.pt'/'converted.weights' in a root directory seems to be not intuitive and convenient.
I propose to save converted file side by side with the original one, but with new extension.

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

This PR improves the file naming for model conversion in the yolov3 repository.

📊 Key Changes

• Changed the output file naming convention when converting models.
• Instead of generic 'converted' filenames, the output files retain their original base names and only their extensions change to reflect the new format (.pt for PyTorch and .weights for Darknet).

🎯 Purpose & Impact

• Clarity: The new naming prevents confusion by clearly linking the output files to their original input files.
• Efficiency: Users can easily identify converted models, streamlining the workflow when working with multiple models.
• No more ambiguity: The change eliminates potential issues with multiple conversions leading to files with identical names, reducing the risk of overwriting important files.

[glenn-jocher]

Sounds good. Thanks for updating the README!