docs: add sample image download and sv.plot_image() to detect_and_annotate tutorial

[PatelPrem21]

…otate tutorial

Before submitting

• Self-reviewed the code
• Updated documentation, follow Google-style
• Added docs entry for autogeneration (if new functions/classes)
• Added/updated tests
• All tests pass locally

Description

New users following the tutorial had no image to test with and
didn't know sv.plot_image() existed. Added the official dog.jpeg
sample image download command and plot_image() call so the tutorial
is fully self-contained.

Closes #1830

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
  -[X] 📝 Documentation update
• 🧪 Test update
• 🔨 Refactoring (no functional changes)
• ⚡ Performance improvement
• 🔧 Chore (dependencies, configs, etc.)

Motivation and Context

Closes #(issue)

Changes Made

Testing

• I have tested this code locally
• I have added unit tests that prove my fix is effective or that my feature works
• All new and existing tests pass

Google Colab (optional)

Colab link:

Screenshots/Videos (optional)

Additional Notes

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