Implementing .gitlab-ci.yml

What this post added

This post details the technical implementation of migrating GitLab CI jobs from a UI-based definition to a `.gitlab-ci.yml` file. It explains the schema change where GitLab now sends the `.gitlab-ci.yml` content along with the webhook to the CI Coordinator. It also outlines the migration strategy, including automatic conversion of existing UI-defined jobs to YAML and the process for users to adopt the new style by copy-pasting the generated YAML file. An example `.gitlab-ci.yml` for a Ruby on Rails project is provided, along with an updated proposal for the file syntax.