Update custom metrics docs to reflect move to Core

The custom metrics feature has been moved to GitLab Core.

doc/user/project/integrations/prometheus.md

@@ -13,7 +13,7 @@ There are two ways to set up Prometheus integration, depending on where your app
 - For deployments on Kubernetes, GitLab can automatically [deploy and manage Prometheus](#managed-prometheus-on-kubernetes).
 - For other deployment targets, simply [specify the Prometheus server](#manual-configuration-of-prometheus).
 
-Once enabled, GitLab will automatically detect metrics from known services in the [metric library](#monitoring-cicd-environments). You are also able to [add your own metrics](#adding-additional-metrics-premium) as well.
+Once enabled, GitLab will automatically detect metrics from known services in the [metric library](#monitoring-cicd-environments). You can also [add your own metrics](#adding-custom-metrics).
 
 ## Enabling Prometheus Integration
 
@@ -132,9 +132,10 @@ GitLab will automatically scan the Prometheus server for metrics from known serv
 
 You can view the performance dashboard for an environment by [clicking on the monitoring button](../../../ci/environments.md#monitoring-environments).
 
-### Adding additional metrics **(PREMIUM)**
+### Adding custom metrics
 
-> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/3799) in [GitLab Premium](https://about.gitlab.com/pricing/) 10.6.
+> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/3799) in [GitLab Premium](https://about.gitlab.com/pricing/) 10.6.
+> - [Moved](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/28527) to [GitLab Core](https://about.gitlab.com/pricing/) 12.10.
 
 Custom metrics can be monitored by adding them on the monitoring dashboard page. Once saved, they will be displayed on the environment performance dashboard provided that either:
 
@@ -191,8 +192,8 @@ You may create a new file from scratch or duplicate a GitLab-defined Prometheus
 dashboard.
 
 NOTE: **Note:**
-The custom metrics as defined below do not support alerts, unlike
-[additional metrics](#adding-additional-metrics-premium).
+The metrics as defined below do not support alerts, unlike
+[custom metrics](#adding-custom-metrics).
 
 #### Adding a new dashboard to your project
 
@@ -654,9 +655,9 @@ Data from Prometheus charts on the metrics dashboard can be downloaded as CSV.
 
 #### Managed Prometheus instances
 
-> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/6590) in [GitLab Ultimate](https://about.gitlab.com/pricing/) 11.2 for [custom metrics](#adding-additional-metrics-premium), and 11.3 for [library metrics](prometheus_library/metrics.md).
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/6590) in [GitLab Ultimate](https://about.gitlab.com/pricing/) 11.2 for [custom metrics](#adding-custom-metrics), and 11.3 for [library metrics](prometheus_library/metrics.md).
 
-For managed Prometheus instances using auto configuration, alerts for metrics [can be configured](#adding-additional-metrics-premium) directly in the performance dashboard.
+For managed Prometheus instances using auto configuration, alerts for metrics [can be configured](#adding-custom-metrics) directly in the performance dashboard.
 
 To set an alert:
 

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

@@ -3,7 +3,7 @@
 .col-lg-3
   %p
     = s_('PrometheusService|Custom metrics require Prometheus installed on a cluster with environment scope "*" OR a manually configured Prometheus to be available.')
-    = link_to s_('PrometheusService|More information'), help_page_path('user/project/integrations/prometheus', anchor: 'adding-additional-metrics-premium'), target: '_blank', rel: "noopener noreferrer"
+    = link_to s_('PrometheusService|More information'), help_page_path('user/project/integrations/prometheus', anchor: 'adding-custom-metrics'), target: '_blank', rel: "noopener noreferrer"
 
 .col-lg-9
   .card.custom-monitored-metrics.js-panel-custom-monitored-metrics{ data: { active_custom_metrics: project_prometheus_metrics_path(project), environments_data: environments_list_data, service_active: "#{@service.active}" } }