弃用对RHEL 7和RHEL 7兼容操作系统的支持

Background

上游在 17.7 中弃用了对 RHEL 7和RHEL 7兼容操作系统的支持

Todos

• 调整构建项目，废弃RHEL 7 系列安装包的构建任务 @kangliu
• 更新相关文档 @majinghe

Related links

• https://gitlab.com/gitlab-org/gitlab/-/merge_requests/173537
• https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/8714
• https://docs.gitlab.com/ee/administration/package_information/supported_os.html#os-versions-that-are-no-longer-supported