Can one change a group to a subgroup in GitLab?

For more current information, this feature has now been added to gitlab and you can transfer an existing group to become a subgroup of a different existing group.

The linked issue in @Zeta 's answer was closed and this issue (https://gitlab.com/gitlab-org/gitlab-ce/issues/31885) became the primary issue on this topic.

At the time of writing this, the method to change a group to a subgroup is as follows:

1. go to the group you want to turn into a subgroup.
2. Go to the general settings of that group.
3. Expand "Path, transfer, remove".
4. Under this is a "Transfer group" box where you select your desired parent group that you manage.
5. After specifying the desired parent group, hit transfer group and it should be moved to the appropriate path.

Gitlab Notes (taken from gitlab web interface):

• Be careful. Changing a group's parent can have unintended side effects.
• You can only transfer the group to a group you manage.
• You will still need to update all local repositories.
• If the parent group's visibility is lower than the group current visibility, visibility levels for subgroups and projects will be changed to match the new parent group's visibility.