message: Monitoring: Fix sidebar SERVER_FLAGS.alertManagerBaseURL check
  It looks like this check was accidentally removed.
diff: @@ -286,7 +286,7 @@ const MonitoringNavSection_ = ({ urls }) => {
  const prometheusURL = urls[MonitoringRoutes.Prometheus];
  const grafanaURL = urls[MonitoringRoutes.Grafana];
  const kibanaURL = urls[MonitoringRoutes.Kibana];
  - return window.SERVER_FLAGS.prometheusBaseURL || prometheusURL || grafanaURL || kibanaURL
  + return window.SERVER_FLAGS.prometheusBaseURL || window.SERVER_FLAGS.alertManagerBaseURL || prometheusURL || grafanaURL || kibanaURL
  ? <NavSection title="Monitoring">
  {window.SERVER_FLAGS.prometheusBaseURL && <HrefLink href="/monitoring/alerts" name="Alerts" startsWith={monitoringAlertsStartsWith} />}
  {window.SERVER_FLAGS.alertManagerBaseURL && <HrefLink href="/monitoring/silences" name="Silences" />}
  