Add latest changes from gitlab-org/gitlab@12-8-stable-ee

changelogs/unreleased/update-graphicsmagick-to-1-3-34.yml

changelogs/unreleased/update-handlebarsjs.yml

changelogs/unreleased/update_cluster-applications_v0-7-0.yml

changelogs/unreleased/weimeng-upgrade-omniauth-github.yml

changelogs/unreleased/xanf-prohibit-outer-forks.yml

changelogs/unreleased/youtrack-issue-pattern.yml