Reviewer roulette via Danger

What does this MR do?

(Tries to) add reviewer roulette via Danger. The idea is that danger can scan the MR and determine what reviews it needs. Once decided, it can randomly pick a reviewer and maintainer for each category, perhaps taking OOO status into account along with any other information. It could even take CODEOWNERS information into account.

The final choice of which reviewers to use should remain with the author of the merge request - these are just suggestions to ease selection when the author doesn't have a strong opinion.

I'm new to danger - let's see what I can do!

What are the relevant issue numbers?

Closes #56087 (closed)

Does this MR meet the acceptance criteria?

• [-] Changelog entry added, if necessary
• Documentation created/updated via this MR
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the style guides
• Security reports checked/validated by reviewer

danger/changelog/Dangerfile

@@ -16,16 +16,12 @@ consider adding any of the %<labels>s labels.
 #{SEE_DOC}
 MSG
 
-def ee?
-  ENV['CI_PROJECT_NAME'] == 'gitlab-ee' || File.exist?('../../CHANGELOG-EE.md')
-end
-
 def ee_changelog?(changelog_path)
   changelog_path =~ /unreleased-ee/
 end
 
 def ce_port_changelog?(changelog_path)
-  ee? && !ee_changelog?(changelog_path)
+  helper.ee? && !ee_changelog?(changelog_path)
 end
 
 def check_changelog(path)