Comment by mydigitalself

Yip, GitLab has subgroups that allow you to organise projects like that, although it's not available for /user namespace, so you can create

groupa/subgroup/repo groupa/subgroup/subgroup/subgroup/etc/repo

https://docs.gitlab.com/ce/user/group/subgroups/

This feature is available for free on GitLab.com and is available for free in self-hosted GitLab CE