www/gitlab: major upgrade to 17.3.1

This commit includes also a suggestion from Robert Nagy <robert@openbsd.org>
to use the git version from gitlab in the gitaly port which is now required.
Thanks again for this contributation!

Put the gitlab and git version into a common Makefile that is included in every
port that requires the same version like gitlab has.

Changes: https://about.gitlab.com/releases/2024/07/18/gitlab-17-2-released/
Changes: https://about.gitlab.com/releases/2024/08/15/gitlab-17-3-released/