Add support for advanced CI/CD config extension with `extends:`
What does this MR do?
This adds support for extends:
keyword in .gitlab-ci.yml
that makes it possible to use inheritance-like feature to reuse YAML configuration.
What are the relevant issue numbers?
Closes gitlab-org/gitlab-ee#6136
Does this MR meet the acceptance criteria?
-
Changelog entry added, if necessary -
Documentation created/updated -
Tests added for this feature/bug -
Conforms to the code review guidelines -
Conforms to the merge request performance guidelines -
Conforms to the style guides -
Conforms to the database guides
Edited by Grzegorz Bizon