Add icon for billing

app/views/layouts/nav/_new_profile_sidebar.html.haml

@@ -20,8 +20,10 @@
             Account
       - if current_application_settings.should_check_namespace_plan?
         = nav_link(controller: :billings) do
-          = link_to profile_billings_path, title: 'Billing' do
-            %span
+          = sidebar_link profile_billings_path, title: _('Billing') do
+            .nav-icon-container
+              = custom_icon('credit_card')
+            %span.nav-item-name
               Billing
       - if current_application_settings.user_oauth_applications?
         = nav_link(controller: 'oauth/applications') do

app/views/shared/icons/_credit_card.svg

+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16"><path d="M14 5a1 1 0 0 0-1-1H3a1 1 0 0 0-1 1h12zm0 3H2v3a1 1 0 0 0 1 1h10a1 1 0 0 0 1-1V8zM3 2h10a3 3 0 0 1 3 3v6a3 3 0 0 1-3 3H3a3 3 0 0 1-3-3V5a3 3 0 0 1 3-3zm6.5 8h3a.5.5 0 1 1 0 1h-3a.5.5 0 1 1 0-1z"/></svg>