Running CI jobs in sequential, parallel, and custom orders

What this post added

This post introduces and explains the use of `stages` for sequential job execution, `needs` for defining job dependencies and enabling Directed Acyclic Graphs (DAGs) for more flexible pipeline execution, and the `image` keyword to specify custom Docker images (like `alpine`) for CI jobs to reduce build times. It also covers artifact management with `paths` and `expire_in`, and the use of `before_script` for setup tasks within specific jobs.