Update Group Import/Export documentation
The following discussions from !20353 (merged) should be addressed:
> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/20353) in GitLab 12.8 as an experimental feature. May change in future releases.
Even better, the issue.
Group Import/Export allows for exporting group structure and importing it at a new location. Used with [Project Import/Export](project_import_export.md), you can preserve connections with group-level relationships. For example, connection between a project issue and group epic.
Group exports include the following: - Group milestones - Group boards - Group labels - Group badges - Group members - Sub-groups. Each sub-group includes all data above
Time spent on exporting a group may vary depending on a size of the group. This endpoint returns either: - The exported archive when available. - 404 is returned otherwise.