Add plugin development guide documentation

[sweetytweety2406-wq]

Description

Added a complete plugin development guide documentation for OpenAgent Eval. This guide explains the plugin architecture, creating custom metrics, registering LLM providers, configuring entry points, testing plugins locally, best practices, and common pitfalls.

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)
• Documentation update
• Refactoring (no functional changes)
• Test update
• CI/CD update

Related Issues

Closes #108

How Has This Been Tested?

Documentation changes were verified by checking the MkDocs documentation build locally.

• Unit tests pass (uv run pytest)
• Linter passes (uv run ruff check .)
• Type checker passes (uv run mypy openagent_eval/)
• Manual testing performed

Checklist

• My code follows the project's coding standards
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Screenshots (if applicable)

Not applicable.

Additional Notes

Added a beginner-friendly plugin development guide to help contributors understand how to create and register plugins in OpenAgent Eval.

[github-actions]

🎉 Congratulations @sweetytweety2406-wq!

Your pull request has been successfully merged into main. 🚀

Thank you for contributing to OpenAgentHQ and helping improve the project.

We truly appreciate your contribution and hope to see you back with more amazing PRs!

Happy Open Sourcing! ❤️

🌟 This is your first merged contribution to this repository.
Welcome to the OpenAgentHQ contributors family!

[sweetytweety2406-wq]

@himanshu231204 Thank you sir for reviewing and merging my contribution. I appreciate the feedback and the opportunity to contribute to OpenAgentHQ. Looking forward to contributing again!

[himanshu231204]

@himanshu231204 Thank you sir for reviewing and merging my contribution. I appreciate the feedback and the opportunity to contribute to OpenAgentHQ. Looking forward to contributing again!

Thanks for contribution . you can tag us on twitter & LinkedIn to show your contribution in this repo.

we have one more ongoing project. check out the "modeldoc" from the organization. looking forward for your contribution.