Merge branch 'docs-agents-md-mr-template-rule' into 'main'

Add merge request template rule to AGENTS.md

See merge request https://gitlab.com/gitlab-org/gitlab-runner/-/merge_requests/7147

Merged-by: Adebayo Adesanya <aadesanya@gitlab.com>
Approved-by: Adebayo Adesanya <aadesanya@gitlab.com>
Reviewed-by: Adebayo Adesanya <aadesanya@gitlab.com>
Co-authored-by: Ben Bodenmiller <bbodenmiller@gmail.com>