Add parent-child pipeline relationship spec

What does this MR do?

This MR contains 2 E2E tests for parent-child pipelines relationship

• E2E test for parent and child pipeline without "strategy: depend" relationship
• E2E test for parent and child pipeline with "strategy: depend" relationship

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content