Add common evaluation workflow examples to docs/examples.md

[himanshu231204]

Description

The examples documentation page (\docs/examples.md) could be expanded with real-world workflow examples that users can copy-paste to get started quickly.

What to Add

Add short, focused code examples showing:

1. Quick eval from Python — using the Python SDK directly
2. Compare two models — running evaluations with GPT-4o vs Claude and comparing results
3. Custom metric — creating and registering a simple custom metric
4. CI/CD integration — running eval in a GitHub Action and checking thresholds
5. Batch evaluation — running multiple configs programmatically

Files to Look At

• \docs/examples.md\ — where to add
• \examples/rag_evaluation_tutorial.ipynb\ — existing notebook for reference
• \openagent_eval/core/engine.py\ — for accurate API examples

Good First Issue ✅

A documentation task that teaches you the core APIs.