move additional_metrics.yaml into prometheus/ config folder

lib/gitlab/prometheus/additional_metrics_parser.rb

@@ -27,7 +27,7 @@ module Gitlab
       end
 
       def load_yaml_file
-        YAML.load_file(Rails.root.join('config/additional_metrics.yml'))
+        YAML.load_file(Rails.root.join('config/prometheus/additional_metrics.yml'))
       end
     end
   end

spec/models/environment_spec.rb

@@ -475,7 +475,7 @@ describe Environment, models: true do
       end
 
       it 'returns the additional metrics from the deployment service' do
-        expect(environment.prometheus_service).to receive(:additional_environment_metrics)
+        expect(project.prometheus_service).to receive(:additional_environment_metrics)
                                                 .with(environment)
                                                 .and_return(:fake_metrics)