Configure GitLab CI parent-child pipelines where a parent pipeline dynamically generates a child pipeline YAML based on changed paths and triggers it with the artifact strategy

Verified steps

1. In the parent pipeline, define a generate job that runs a script inspecting git diff --name-only against the target branch and writes a child pipeline YAML to a file, then declares the file as an artifact
2. Add a trigger job in the parent that uses trigger: include: - artifact: child-pipeline.yml job: generate strategy: depend so the parent waits for the child and propagates its status
3. In the generator script, conditionally include only the pipeline stages relevant to changed directories, emitting a minimal YAML; use YAML anchors or extends in the generated file to reuse shared job templates
4. Pass CI variables from the parent to the child via trigger: variables: so the child inherits environment context like target cluster, registry URL, and deploy token without hardcoding
5. Configure the child pipeline to use needs: [] on independent jobs to enable DAG parallelism; add resource_group: keywords on deploy jobs to serialize per-environment
6. Add a downstream pipeline notification job in the parent that posts the child pipeline web URL to a merge request comment using the GitLab API if the trigger strategy fails