Include machine learning settings type

On the Configuration settings page three settings appeared without
description:

* Comments Summary: No description.
* Related Content: No description.
* Tags: No description.

These settings are related with the AI / Machine learning feature. They
only should appear on AI / Machine learning setting page when the
feature is enabled.

app/models/setting.rb

@@ -8,7 +8,7 @@ class Setting < ApplicationRecord
   end
 
   def type
-    if %w[feature process proposals map html homepage uploads sdg].include? prefix
+    if %w[feature process proposals map html homepage uploads sdg machine_learning].include? prefix
       prefix
     elsif %w[remote_census].include? prefix
       key.rpartition(".").first

spec/system/admin/settings_spec.rb

@@ -346,4 +346,26 @@ describe "Admin settings", :admin do
       expect(page).to have_css "h2", exact_text: "SDG configuration"
     end
   end
+
+  describe "Machine learning settings" do
+    scenario "show the machine learning feature but not its settings" do
+      Setting["feature.machine_learning"] = true
+
+      visit admin_settings_path
+
+      expect(page).not_to have_content "Machine Learning"
+      expect(page).not_to have_content "Comments Summary"
+      expect(page).not_to have_content "Related Content"
+      expect(page).not_to have_content "Tags"
+      expect(page).not_to have_css ".translation_missing"
+
+      click_link "Features"
+
+      expect(page).to have_content "Machine Learning"
+      expect(page).not_to have_content "Comments Summary"
+      expect(page).not_to have_content "Related Content"
+      expect(page).not_to have_content "Tags"
+      expect(page).not_to have_css ".translation_missing"
+    end
+  end
 end