I would propose an extension of the existing gitlab integration.
Create Issues from ticket and link them (linking somewhat exists already)
Issues should be possible to be created for a specific project.
Possibly right where it currently is possible to link issues to a ticket.
Should be possible to select project and create issue.
Maybe not necessarily creating issue in zammad, instead using already existing interface in gitlab.
I will probably start implementing this feature, but I would love to hear feedback and different perspectives/options. I also would love for this to be added.