Move scripts used in CI to the new location (#5198)

* Move CI scripts and update references

* Update paths in .gitlab-ci.yml

* Removed outdated entries from CODEOWNERS

polkadot/scripts/ci/changelog/lib/changelog.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+# A Class to find Substrate references
+class SubRef
+  require 'octokit'
+  require 'toml'
+
+  attr_reader :client, :repository
+
+  def initialize(github_repo)
+    @client = Octokit::Client.new(
+      access_token: ENV['GITHUB_TOKEN']
+    )
+    @repository = @client.repository(github_repo)
+  end
+
+  # This function checks the Cargo.lock of a given
+  # Rust project, for a given package, and fetches
+  # the dependency git ref.
+  def get_dependency_reference(ref, package)
+    cargo = TOML::Parser.new(
+      Base64.decode64(
+        @client.contents(
+          @repository.full_name,
+          path: 'Cargo.lock',
+          query: { ref: ref.to_s }
+        ).content
+      )
+    ).parsed
+    cargo['package'].find { |p| p['name'] == package }['source'].split('#').last
+  end
+
+  # Get the git ref of the last release for the repo.
+  # repo is given in the form paritytech/polkadot
+  def get_last_ref()
+    'refs/tags/' + @client.latest_release(@repository.full_name).tag_name
+  end
+end