Integrating GitLab CI with GitLab to enable distributed builds

What this post added

This post introduces the integration of GitLab CI with GitLab, enabling distributed builds by default. It outlines the benefits of this integration, including single sign-on with GitLab credentials, UI integration showing accessible projects, and simplified setup. The architecture is described as a clean separation using GitLab's public API, with GitLab CI as a rack application. A key concept introduced is the split into coordinators and runners, where runners perform builds on separate machines to avoid security risks associated with running tests on the source code server. This design aims to encourage best practices for CI/CD.