Resolve "Un-vendor CI templates"
What does this MR do?
The other side of this work gitlab-ci-yml!204 (merged)
mv vendor/gitlab-ci-yml lib/gitlab/ci/templates
- add a spec that validates all the templates in this repo (equivalent of the spec we had in https://gitlab.com/gitlab-org/gitlab-ci-yml)
- update all docs so they no longer mention the old templates repo
What are the relevant issue numbers?
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
Closes #50289 (closed)