Thank you for your votes and comments on this issue.
We would like to inform you that the official support for GitLab will be available in the upcoming 8.14.0 release of Jira Server and Data Center.
We will change the status of this suggestion when Jira 8.14 is available. At the moment, you can read our latest EAP version for Integrating Jira with GitLab.
Senior Product Manager, Jira Server and Data Center