Implementing .gitlab-ci.yml

This post details the technical implementation of migrating GitLab CI from UI-defined jobs to a `.gitlab-ci.yml` file. It outlines the schema change where the `.gitlab-ci.yml` content is sent to the CI Coordinator, explains the migration strategy of converting existing UI jobs to YAML and providing a download option, and presents an example of the new YAML syntax for a Ruby on Rails project, including an update to simplify the syntax.