Require prometheus only for querying endpoints

app/controllers/projects/prometheus/metrics_controller.rb

@@ -2,7 +2,7 @@ module Projects
   module Prometheus
     class MetricsController < Projects::ApplicationController
       before_action :authorize_admin_project!
-      before_action :require_prometheus_metrics!
+      before_action :require_prometheus_metrics!, only: [:active_common, :validate_query]
 
       def active_common
         respond_to do |format|

lib/gitlab/prometheus/queries/matched_metrics_query.rb

@@ -18,7 +18,7 @@ module Gitlab
         private
 
         def groups_data
-          metrics_groups = groups_with_active_metrics(Gitlab::Prometheus::MetricGroup.all)
+          metrics_groups = groups_with_active_metrics(Gitlab::Prometheus::MetricGroup.common_metrics)
           lookup = active_series_lookup(metrics_groups)
 
           groups = {}