Ensure that dynamic child pipeline depends explicitly on the generator job

Problem

When using "Dynamic Child Pipeline" feature we are not strictly checking whether the job generating the configurations is a dependency for the trigger job using the generated configuration.

The following snippet has child-pipeline job running before generate-config. This will cause the following behavior:

1. Parent pipeline is created successfully
2. Parent pipeline's jobs are enqueued
3. Trigger job child-pipeline runs and attempts to create a child pipeline
4. The child pipeline fails with error Job generate-config not found in parent pipeline or does not have artifacts
5. Trigger job fails by consequence
6. Parent pipeline fails by consequence

child-pipeline:
  stage: test
  trigger:
    include:
      - artifact: generated-config.yml
        job: generate-config

generate-config:
  stage: deploy
  script: generate-ci-config > generated-config.yml
  when: always
  artifacts:
    paths:
      - generated-config.yml

Expected behavior

1. Parent pipeline fails immediately showing an error child-pipeline does not depend on a generate-config job

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Original discussion: !23790 (comment 298174064)