Add parent and child pipelines CI files.

.child-ci.yml

+child_job:
+  stage: test
+  tags: ["pipelines-dependent-relationship-3f0753bb0166703f"]
+  script: echo "Child job done!"
+

.gitlab-ci.yml

+stages:
+  - test
+  - deploy
+
+job1:
+  stage: test
+  trigger:
+    include: ".child-ci.yml"
+    strategy: depend
+
+job2:
+  stage: deploy
+  tags: ["pipelines-dependent-relationship-3f0753bb0166703f"]
+  script: echo "parent deploy done"
+