Add help item to bottom of signed out top nav

https://gitlab.com/gitlab-org/gitlab/-/issues/301143#note_561841810

app/helpers/nav/top_nav_helper.rb

@@ -44,6 +44,13 @@ module Nav
           **snippets_menu_item_attrs
         )
       end
+
+      builder.add_secondary_menu_item(
+        id: 'help',
+        title: _('Help'),
+        icon: 'question-o',
+        href: help_path
+      )
     end
 
     def build_view_model(builder:, project:, group:)

spec/helpers/nav/top_nav_helper_spec.rb

@@ -94,6 +94,18 @@ RSpec.describe Nav::TopNavHelper do
         ]
         expect(subject[:shortcuts]).to eq(expected_shortcuts)
       end
+
+      it 'has expected :secondary' do
+        expected_secondary = [
+          ::Gitlab::Nav::TopNavMenuItem.build(
+            href: '/help',
+            id: 'help',
+            title: 'Help',
+            icon: 'question-o'
+          )
+        ]
+        expect(subject[:secondary]).to eq(expected_secondary)
+      end
     end
 
     context 'when current_user is non-admin' do