Summary:
This is already supported, when running Flipper on Mac, so just need update schema.
One use case for `MacOS`, is to have a static plugin available to users before they launch any app/device. So this can be used as Welcome plugin, Documentation or any other "static" plugin not requiring any other device except the one running Flipper Desktop.
## Changelog
- add `MacOS` to supported devices
Pull Request resolved: https://github.com/facebook/flipper/pull/3648
Test Plan: - Script `lint` should pass.
Reviewed By: antonk52
Differential Revision: D35810577
Pulled By: lblasa
fbshipit-source-id: e1a2948fdf67535d28b68eeab649214b44ebcf9c
e7c56045f5