feat: add korean(ko) locale (#4332)

packages/netlify-cms-locales/src/index.js

@@ -20,3 +20,4 @@ export { default as tr } from './tr';
 export { default as uk } from './uk';
 export { default as vi } from './vi';
 export { default as zh_Hant } from './zh_Hant';
+export { default as ko } from './ko';