Fix performance bar warnings when Rugged is disabled

`detailed_metric.vue` was attempting to read the `duration` field even
when the metric did not exist in the JSON payload. We now check for the
existence of the metrics before attempting to display the value.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/65491

app/assets/javascripts/performance_bar/components/detailed_metric.vue

@@ -44,7 +44,7 @@ export default {
 </script>
 <template>
   <div
-    v-if="currentRequest.details"
+    v-if="currentRequest.details && metricDetails"
     :id="`peek-view-${metric}`"
     class="view qa-performance-bar-detailed-metric"
   >