Fix links to Prometheus Metrics Library

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

app/views/projects/services/prometheus/_metrics.html.haml

 - project = local_assigns.fetch(:project)
 
-.card.js-panel-monitored-metrics{ data: { active_metrics: active_common_project_prometheus_metrics_path(project, :json), metrics_help_path: help_page_path('user/project/integrations/prometheus_library/metrics') } }
+.card.js-panel-monitored-metrics{ data: { active_metrics: active_common_project_prometheus_metrics_path(project, :json), metrics_help_path: help_page_path('user/project/integrations/prometheus_library/index') } }
   .card-header
     = s_('PrometheusService|Common metrics')
     %span.badge.badge-pill.js-monitored-count 0

app/views/projects/services/prometheus/_show.html.haml

@@ -4,7 +4,7 @@
       = s_('PrometheusService|Metrics')
     %p
       = s_('PrometheusService|Common metrics are automatically monitored based on a library of metrics from popular exporters.')
-      = link_to s_('PrometheusService|More information'), help_page_path('user/project/integrations/prometheus_library/metrics'), target: '_blank', rel: "noopener noreferrer"
+      = link_to s_('PrometheusService|More information'), help_page_path('user/project/integrations/prometheus_library/index'), target: '_blank', rel: "noopener noreferrer"
 
   .col-lg-9
     = render 'projects/services/prometheus/metrics', project: @project

doc/user/project/integrations/prometheus.md

@@ -87,7 +87,7 @@ to integrate with.
 Once configured, GitLab will attempt to retrieve performance metrics for any
 environment which has had a successful deployment.
 
-GitLab will automatically scan the Prometheus server for metrics from known serves like Kubernetes and NGINX, and attempt to identify individual environment. The supported metrics and scan process is detailed in our [Prometheus Metric Library documentation](prometheus_library/metrics.html). 
+GitLab will automatically scan the Prometheus server for metrics from known serves like Kubernetes and NGINX, and attempt to identify individual environment. The supported metrics and scan process is detailed in our [Prometheus Metric Library documentation](prometheus_library/index.md).
 
 You can view the performance dashboard for an environment by [clicking on the monitoring button](../../../ci/environments.md#monitoring-environments).