Migrate customers unavailable to shared haml alert

ee/app/views/shared/billings/customers_dot_unavailable.html.haml

 - page_title _("Billing")
 
-.gl-alert.gl-alert-danger.gl-mb-5
-  = sprite_icon('error', size: 16, css_class: 'gl-icon gl-alert-icon')
-  .gl-alert-content
-    .gl-alert-title
-      = _('Subscription service outage')
-    .gl-alert-body
-      = html_escape(_("The GitLab subscription service (customers.gitlab.com) is currently experiencing an outage. You can monitor the status and get updates at %{linkStart}status.gitlab.com%{linkEnd}.")) % { linkStart: "<a href=\"#{::EE::GITLAB_COM_STATUS_URL}\">".html_safe, linkEnd: '</a>'.html_safe }
+= render 'shared/global_alert',
+  title: _('Subscription service outage'),
+  variant: :danger,
+  is_contained: true,
+  alert_class: 'gl-mb-5',
+  dismissible: false do
+  .gl-alert-body
+    = html_escape(_("The GitLab subscription service (customers.gitlab.com) is currently experiencing an outage. You can monitor the status and get updates at %{linkStart}status.gitlab.com%{linkEnd}.")) % { linkStart: "<a href=\"#{::EE::GITLAB_COM_STATUS_URL}\">".html_safe, linkEnd: '</a>'.html_safe }