Set some GitLab default settings for new projects and users in config file

Still tweaking GitLab setup. Since our intention is to only use GitLab for internal projects for now, the idea is to pair down the available options for new users and projects. We don't need issues, wikis, pipelines,ci, or service desk for every single project. Those tools can still be enabled on a case by case basis. We want to be very intentional and minimal about creating groups so we'll disable that option for new users for now. Also in this commit we are setting the default theme for new users. All users can still change this in their own profile.