Merge branch 'mjang-manage-access-subgroup-page-metadata' into 'master'

Update metadata on manage access subgroup doc

See merge request gitlab-org/gitlab!55651

doc/user/group/subgroups/index.md

 ---
-stage: none
-group: unassigned
+stage: Manage
+group: Access
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 type: reference, howto, concepts
 ---