Require 2 approvals with "smart" branch protection

This issue is considered done when we have the proper branch protection and GitHub Actions in place such that 2 CODEOWNER approvals are required or only 1 is required if the author is a CODEOWNER.

Per discussion in https://github.com/filecoin-project/github-mgmt/pull/61#issuecomment-2313319725 , we want to ideally have 2 approvers to changes to this repo, but to make this not too burdensome, we ideally want it so only one approval is needed if the author is a CODEOWNER.

This is a followup task for https://github.com/filecoin-project/github-mgmt/issues/47