maint: Add AGENTS.md file

[MikeGoldsmith]

Description

Adds AGENTS.md file. The intent of this file is to:

• Make sure there is a human in the loop when creating a PR or posting issue comments.
• Make sure that commits created primarily by an agent are easily identifiable by reviewers

This is heavily inspired on the Open Policy Agent AGENTS.md file and the Fedora AI-assisted contributions policy.

This only affects agents that are compliant with the AGENTS.md file (see https://agents.md/ for list of tools that support it), as well as Claude Code using this workaround.

This has been added to other projects, such as the Collector.

This is just a barebones version and we can add more stuff like setup commands or code style guidance later.

Type of change

Please delete options that are not relevant.

• 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)
• This change requires a documentation update

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[MikeGoldsmith]

Closing as dup of #4233