Change metadata for import/export

doc/user/project/settings/import_export.md

 ---
-stage: Create
-group: Source Code
+stage: Manage
+group: Import
 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/#designated-technical-writers"
 type: reference, howto
 ---