help: add a custom help dropdown in dossier context

spec/views/layouts/_new_header_spec.rb

@@ -16,6 +16,10 @@ describe 'layouts/_new_header.html.haml', type: :view do
 
       it { is_expected.to have_css("a.header-logo[href=\"#{dossiers_path}\"]") }
       it { is_expected.to have_link("Dossiers", href: dossiers_path) }
+
+      it 'displays the Help button' do
+        expect(subject).to have_link("Aide", href: FAQ_URL)
+      end
     end
 
     context 'when rendering for gestionnaire' do