Gogs is a free project and repository management application Application details written in Go distributed under the MIT License comparable with gitlab very low system requirements Reproducible: Always
It is already in the tree of archlinux. Their experience could be a good start for a new ebuild. https://aur.archlinux.org/packages/gogs-git/
This has been in GURU for a few years but there's currently no maintainer. I just submitted a final security bump on it but it's been last-rited and will be dropped in a few weeks. If any of you are interested in taking it over, feel free: https://github.com/gentoo/guru/tree/master/www-apps/gogs