Add AI coding agent instructions to AGENTS.md

[ewega]

⚠️ Pre Checklist

Please complete ALL items in this checklist, and remove before submitting

• [x] I have read through the Contributing Documentation.
• [x] I have added relevant tests.
• [x] I have added relevant documentation.
• [ ] I will add labels to the PR, such as pr-type/bug-fix, pr-type/feature-development, etc.

Summary

Adds an AGENTS.md file for agent onboarding to the project

Does this close any open issues?

Closes #8655

Screenshots

N/A

Other Information

This is one of many methods to onboard agents onto the project for any contributor. It is optimal as it is standardized, but there are many ways to onboard different agents (e.g. .github/copilot-instructions.md, CLAUDE.md).

Would like input from major contributors on if there is any specific information we should add or remove