addUserToGitlab() should not add the user to the project unconditionally
in the last step of addUserToGitlab(), the user is added to Gitlab's project unconditionally. It should not. Any registered user to JIRA or Gitlab can report an issue to any public project, it doesn't make him a project member.
Users that should be added to the projects are those who are mentioned in the JIRA project's roles (admins and devs, not users)