Move global ci entries handling from legacy to new config
## What does this MR do?
This MR moves responsibility of handling global CI config entries (like `image`, `services`), from legacy `GitlabCiYamlProcessor` to new CI Config
## Why was this MR needed?
This is the next iteration of CI configuration refactoring
## What are the relevant issue numbers?
#15060
## Does this MR meet the acceptance criteria?
- Tests
- [x] Added for this feature/bug
- [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
See merge request !4820
06c7d6f3a8