Use group for Frontend code owners

This increases the maintainability of the Frontend group owners by
utilizing the group `gitlab-org/maintainers/frontend`

.gitlab/CODEOWNERS

@@ -6,9 +6,9 @@
 /doc/ @axil @marcia @eread @mikelewis
 
 # Frontend maintainers should see everything in `app/assets/`
-app/assets/ @ClemMakesApps @fatihacet @filipa @mikegreiling @timzallmann @kushalpandya @pslaughter @wortschi @ntepluhina @iamphill
-*.scss @annabeldunstone @ClemMakesApps @fatihacet @filipa @mikegreiling @timzallmann @kushalpandya @pslaughter @wortschi @ntepluhina @iamphill
-/scripts/frontend/ @ClemMakesApps @fatihacet @filipa @mikegreiling @timzallmann @kushalpandya @pslaughter @wortschi @ntepluhina @iamphill
+app/assets/ @gitlab-org/maintainers/frontend
+*.scss @annabeldunstone @gitlab-org/maintainers/frontend
+/scripts/frontend/ @gitlab-org/maintainers/frontend
 
 # Database maintainers should review changes in `db/`
 db/ @gitlab-org/maintainers/database