fix: remove hardcoded URLs and fix README badges

[deborahjacob-botanu]

Security compliance improvements:

• detector.py: Make AWS metadata endpoint configurable

  • Uses AWS SDK standard env vars (AWS_EC2_METADATA_SERVICE_ENDPOINT)
  • AWS_EC2_METADATA_DISABLED=true to disable metadata calls
  • Validate URL scheme (http/https only)
  • No custom env vars - follows AWS SDK conventions

• README.md: Fix broken badges

  • Remove OpenSSF badge (repo not yet public)
  • Use static Python versions badge
  • Simplify PyPI version badge

Summary

Changes

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• CI / build / tooling

Testing

• Unit tests pass (pytest)
• Lint passes (ruff check)
• Type check passes (mypy)

Checklist

• My code follows the project's coding style
• I have added SPDX headers to new files
• I have added tests for my changes
• I have updated documentation if needed
• All commits are signed off (git commit -s) per the DCO