Pass dependencies to CI configuration nodes

What does this MR do?

This MR makes it possible to pass dependencies to CI configuration nodes.

What are the relevant issue numbers?

See #15060 (closed)

Does this MR meet the acceptance criteria?

• Tests
  • Added for this feature/bug
  • All builds are passing

Added 1419 commits:

• bf9d4c6e...7bbb523b - 1417 commits from branch master
• 6c704fd9 - Inject dependencies into each CI config entry node
• 700078e8 - Rename unspecified and undefined CI config nodes

Added backstage label

Added 1 commit:

• eaf211c2 - Expose compose method in the ci config entry nodes

Added 1 commit:

• 4f837f66 - Remove temporary stub method from ci config nodes

Added 1 commit:

• 30f58cf3 - Add [] method for accessing ci entry dependencies

Added 1 commit:

• 065c0c5a - Make it possible to inherit global ci config nodes

Added 1 commit:

• 36692c88 - Do not override job nodes in legacy ci config code

Added 1 commit:

• 62f704c5 - Make it possible to inherit global ci config nodes

Added 1 commit:

• bd807503 - 1 commit from branch master

Added 1 commit:

• 1255205d - Add method that returns commands for ci job entry

With this solution it is possible to get each configuration entry object with something like:

global = Gitlab::Ci::Config::Node::Global.new(rspec: { script: 'ls' })
global.compose!
script = global[:jobs][:rspec][:script]
script.value
 => ["ls"]
script.description
 => "Commands that will be executed in this job."

Unmarked this merge request as a Work In Progress

Marked the task Added for this feature/bug as completed

Marked the task All builds are passing as completed

Reassigned to @smcgivern

@smcgivern Can you take a look? Thanks in advance.

mentioned in issue #21277 (closed)