Merge branch 'ee-40285-prometheus-loading-screen-no-longer-seems-to-appear' into 'master'

Port of '40285-prometheus-loading-screen-no-longer-seems-to-appear' to EE

See merge request gitlab-org/gitlab-ee!3748

app/views/projects/environments/metrics.html.haml

@@ -15,8 +15,8 @@
 
   #prometheus-graphs{ data: { "settings-path": edit_project_service_path(@project, 'prometheus'),
     "documentation-path": help_page_path('administration/monitoring/prometheus/index.md'),
-    "empty-getting-started-svg-path": image_path('illustrations/monitoring/getting_started'),
-    "empty-loading-svg-path": image_path('illustrations/monitoring/loading'),
-    "empty-unable-to-connect-svg-path": image_path('illustrations/monitoring/unable_to_connect'),
+    "empty-getting-started-svg-path": image_path('illustrations/monitoring/getting_started.svg'),
+    "empty-loading-svg-path": image_path('illustrations/monitoring/loading.svg'),
+    "empty-unable-to-connect-svg-path": image_path('illustrations/monitoring/unable_to_connect.svg'),
     "additional-metrics": additional_metrics_project_environment_path(@project, @environment, format: :json),
     "has-metrics": "#{@environment.has_metrics?}", deployment_endpoint: project_environment_deployments_path(@project, @environment, format: :json) } }