Merge branch '5511-rename-custom-metric-section-headers' into 'master'

Align custom metric section header naming

Closes #5511

See merge request gitlab-org/gitlab-ee!5175

ee/app/models/prometheus_metric.rb

@@ -9,9 +9,9 @@ class PrometheusMetric < ActiveRecord::Base
   validates :unit, presence: true
 
   GROUP_TITLES = {
-    business: _('Business'),
-    response: _('Response'),
-    system: _('System')
+    business: _('Business metrics (Custom)'),
+    response: _('Response metrics (Custom)'),
+    system: _('System metrics (Custom)')
   }.freeze
 
   def group_title

ee/spec/models/prometheus_metric_spec.rb

@@ -17,9 +17,9 @@ describe PrometheusMetric do
       end
     end
 
-    it_behaves_like 'group_title', :business, 'Business'
-    it_behaves_like 'group_title', :response, 'Response'
-    it_behaves_like 'group_title', :system, 'System'
+    it_behaves_like 'group_title', :business, 'Business metrics (Custom)'
+    it_behaves_like 'group_title', :response, 'Response metrics (Custom)'
+    it_behaves_like 'group_title', :system, 'System metrics (Custom)'
   end
 
   describe '#to_query_metric' do