Why we're replacing GitLab CI jobs with .gitlab-ci.yml

This post introduces the adoption of `.gitlab-ci.yml` for defining GitLab CI jobs, replacing the previous form-based script editing. This change brings version control to build scripts, enabling builds for older versions, improved handling of forks, branch-specific builds, a single source of truth for configurations, and build matrices. The post also mentions the deprecation of the existing job editing interface in favor of this new approach starting with GitLab 8.0.