Variable and artifact sharing in GitLab parent-child pipelines

What this post added

This post details how to share variables and artifacts between parent and child GitLab CI/CD pipelines. It introduces the use of `dotenv` reports to save runtime variables and leverage the `needs` keyword (for Premium/Ultimate users) to inherit these variables and artifacts in child pipelines. It also covers triggering child pipelines based on file changes using `rules: changes` and provides examples for sharing custom variables like Docker image tags.