docs: add Kubernetes deployment guide for zero-code instrumentation

[deborahjacob-botanu]

• Add comprehensive kubernetes.md covering OTel Operator, env vars, init containers, and GitOps integration
• Update README with Kubernetes section and simplified examples
• Update docs index with Kubernetes link and cleaner quick start

Supports enterprise-scale deployments (2000+ apps) without code changes.

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