DRY development: A cheatsheet on reusability throughout GitLab

This post introduces and details several mechanisms within GitLab CI/CD that promote the DRY (Don't Repeat Yourself) principle to minimize code duplication and standardize knowledge. These include: `include` for modularizing `.gitlab-ci.yml` files, YAML anchors for reducing repeat syntax and extending blocks, `extends` for greater flexibility with includes, `!reference` for reusing keyword configurations, downstream pipelines for microservice isolation, and CI/CD variables for scoped and inheritable configurations. Additionally, it covers description templates, project templates, and file templates for consistent code reviews and project initialization.