[gh-pages] RA: Web documentation for the new "deep learning-based human detection exercise"

[codezerro]

📓 Description:

Create and publish the web documentation for the newly developed deep learning-based human detection exercise in Robotics Academy. This documentation should guide users through uploading their ONNX models, using the code editor for inference, and understanding the webcam-based human detection workflow.

✅ Checklist:

• Add updated description of the exercise
• Document how to upload and use custom ONNX models
• Provide example inference code with pre-processing steps
• Explain the input/output format requirements for ONNX models
• Add UI screenshots or video preview
• Add references link
• Update cover image

[jmplaza]

Fixed in #3140