Tenth Korean l10n work for release 1.18

- Translate concepts/extend-kubenetes/service-catalog.md in Korean (#23233)
- Translate concepts/configuration/secret.md into Korean (#23110)
- Translate tasks/extend-kubernetes/setup-extension-api-server.md into … (#22574)
- Update outdated files in dev-1.18-ko.10 branch (#23013)

Co-authored-by: Seokho Son <shsongist@gmail.com>
Co-authored-by: Jerry Park <jaehwa@gmail.com>
Co-authored-by: santachopa <santachopa@naver.com>

content/ko/docs/concepts/storage/storage-classes.md

@@ -10,8 +10,6 @@ weight: 30
 [볼륨](/ko/docs/concepts/storage/volumes/)과
 [퍼시스턴트 볼륨](/ko/docs/concepts/storage/persistent-volumes)에 익숙해지는 것을 권장한다.
 
-
-
 <!-- body -->
 
 ## 소개