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

* upstream/master: (175 commits)
  Document Repository#keep_around
  Don't garbage collect commits that have related DB records like comments
  Update CHANGELOG
  Update RedCloth to 4.3.2 for CVE-2012-6684
  Fix typo in Merge Requests API documentation
  Downgrade to Redis 3.2.2 due to massive memory leak with Sidekiq
  Enable Style/EmptyLines cop, remove redundant ones
  Update CHANGELOG
  Cache results from jQuery selectors to retrieve namespace name
  Fix import button when import fail due the namespace already been taken
  Fix snippets comments not displayed
  Fix emoji paths in relative root configurations
  Exclude requesters from Project#members, Group#members and User#members
  Upgrade Thin from 1.6.1 to 1.7.0.
  Many squashed commits
  Cache autocomplete results
  Upgrade Sidekiq from 4.1.2 to 4.1.4.
  Upgrade seed-fu from 2.3.5 to 2.3.6
  use has_many relationship with events
  Support creating a todo on issuables via API
  ...

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4964#note_12744656

* master: (352 commits)
  Display last commit of deleted branch in push events (!4699)
  add changelog
  add missing attribute to attr_encrypted so it is fully backwards-compatible
  Add "GitLab team members only" to diagram link
  doc: note that .gitattributes uses default branch
  use the conf lexer so we have highlighted comments
  first draft of docs
  support cgi style options, such as erb?parent=json
  move the path alias to a more appropriate location
  make #custom_language private
  appease rubocop
  add an alias for Snippet#path
  appease rubocop
  check the tag so that an instance will pass too
  fix the spec, using project.change_head
  Revert "bump the master sha for gitlab-test!9"
  bump the master sha for gitlab-test!9
  add custom highlighting via .gitattributes
  Rename Licenses API to License Templates API
  Check for conflict with wiki projects when creating a new project.
  ...

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4964#note_12741046

We store the sizes as a hash from path to bytes like:

``` ruby
{'ci_artifacts.txt' => 27,
 'other_artifacts_0.1.2/another-subdirectory/banana_sample.gif' =>
71759,
 'other_artifacts_0.1.2/doc_sample.txt' => 1314,
 'rails_sample.jpg' => 35255,
 'tests_encoding/utf8 test dir ✓/regular_file_2' => 7}
```

So that it's easier to access than reading gzip file again.

Improve validations and error handling in new CI config entries

## What does this MR do?

This MR improves validation in new CI config.

## Why was this MR needed?

With that it will be easier to handle errors during validation and post-processing.

## What are the relevant issue numbers?

This is a continuation of #15060

See merge request !4560