Add a CODEOWNERS file?

[messense]

There are currently too many email notifications if I watch this repository, can we add a CODEOWNERS file so people will only be pinged when relevant code changes?

See https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners

[Xuanwo]

Nice idea. Let's do this.