Migrate seats_count_alert to global_alert

ee/app/views/layouts/header/_seats_count_alert.html.haml

 - return unless show_seats_count_alert?
 .container.container-limited.pt-3
-  .gl-alert.gl-alert-info.js-approaching-seats-count-threshold{ role: 'alert', data: { dismiss_endpoint: group_callouts_path,
-      feature_id: Users::GroupCalloutsHelper::APPROACHING_SEAT_COUNT_THRESHOLD,
-      group_id: root_namespace.id } }
-    = sprite_icon('information-o', size: 16, css_class: 'gl-icon gl-alert-icon')
-    %button.js-close.gl-alert-dismiss{ type: 'button', 'aria-label' => _('Dismiss'), data: { testid: 'approaching-seats-count-threshold-alert-dismiss' } }
-      = sprite_icon('close', size: 16, css_class: 'gl-icon')
+  = render 'shared/global_alert',
+    alert_class: 'js-approaching-seats-count-threshold',
+    alert_data: { dismiss_endpoint: group_callouts_path, feature_id: Users::GroupCalloutsHelper::APPROACHING_SEAT_COUNT_THRESHOLD, group_id: root_namespace.id },
+    title: _('%{group_name} is approaching the limit of available seats') % { group_name: group_name },
+    close_button_data: { testid: 'approaching-seats-count-threshold-alert-dismiss' } do
     .gl-alert-body
-      %h4.gl-alert-title= _('%{group_name} is approaching the limit of available seats') % { group_name: group_name }
       = _('Your subscription has %{remaining_seats_count} out of %{total_seats_count} seats remaining. Even if you reach the number of seats in your subscription, you can continue to add users, and GitLab will bill you for the overage.') % { remaining_seats_count: remaining_seats_count, total_seats_count: total_seats_count }
       = learn_more_link
     .gl-alert-actions