Add trending links (#16917)

* Add trending links

* Add overriding specific links trendability

* Add link type to preview cards and only trend articles

Change trends review notifications from being sent every 5 minutes to being sent every 2 hours

Change threshold from 5 unique accounts to 15 unique accounts

* Fix tests

spec/helpers/languages_helper_spec.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe LanguagesHelper do
+  describe 'the HUMAN_LOCALES constant' do
+    it 'includes all I18n locales' do
+      expect(described_class::HUMAN_LOCALES.keys).to include(*I18n.available_locales)
+    end
+  end
+
+  describe 'human_locale' do
+    it 'finds the human readable local description from a key' do
+      expect(helper.human_locale(:en)).to eq('English')
+    end
+  end
+end