[chore] address codeowners to reflect current status

[kelset]

Please select one of the following

• I am removing an existing difference between facebook/react-native and microsoft/react-native-macos 👍
• I am cherry-picking a change from Facebook's react-native into microsoft/react-native-macos 👍
• I am making a fix / change for the macOS implementation of react-native
• I am making a change required for Microsoft usage of react-native

Summary

One thing I noticed is that whenever a new PR is opened @alloy gets assigned as codeowner to review. (the reason why it was only him is because the 3 owners were in 3 separate lines, see: https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners)

I've updated the file to reflect the current status (as far as I can tell) of who is in charge of this repo at this point in time.

Changelog

N/A

Test Plan

N/A