Aggreagated metrics add YAML anchors and aliases

To avoid repetitive parts of aggregated metrics definition lets
utilize YAML anchor and aliases feature

lib/gitlab/usage/metrics/aggregates/aggregate.rb

@@ -148,7 +148,7 @@ module Gitlab
           end
 
           def load_yaml_from_path(path)
-            YAML.safe_load(File.read(path))&.map(&:with_indifferent_access)
+            YAML.safe_load(File.read(path), aliases: true)&.map(&:with_indifferent_access)
           end
         end
       end

spec/lib/gitlab/usage/metrics/aggregates/aggregate_spec.rb

@@ -222,6 +222,12 @@ RSpec.describe Gitlab::Usage::Metrics::Aggregates::Aggregate, :clean_gitlab_redi
       end
     end
 
+    it 'allows for YAML aliases in aggregated metrics configs' do
+      expect(YAML).to receive(:safe_load).with(kind_of(String), aliases: true)
+
+      described_class.new(recorded_at)
+    end
+
     describe '.aggregated_metrics_weekly_data' do
       subject(:aggregated_metrics_data) { described_class.new(recorded_at).weekly_data }