Backend: Create `Entry::Node` classes for `spec`
Problem
We need a way to produce a stable hash from CI config spec
entries.
Proposed solution
Let's use the existing pattern of defining subclasses of Entry::Node
that validate and normalize CI configurations.
We can create Gitlab::Ci::Config::Header::Root
as the entry point for validating the header document in a multi-doc CI YAML.
Edited by Fabio Pitino