Migrate historical_max_users metric to Instrumentation class

ee/config/metrics/license/20210204124835_historical_max_users.yml

@@ -7,6 +7,7 @@ product_group: group::license
 product_category: license
 value_type: number
 status: active
+instrumentation_class: HistoricalMaxUsersMetric
 time_frame: none
 data_source: database
 data_category: subscription

ee/lib/ee/gitlab/usage_data.rb

@@ -93,7 +93,7 @@ module EE
             usage_data[:license_md5] = license.md5
             usage_data[:license_id] = license.license_id
             # rubocop: disable UsageData/LargeTable
-            usage_data[:historical_max_users] = license.historical_max
+            usage_data[:historical_max_users] = add_metric("HistoricalMaxUsersMetric")
             # rubocop: enable UsageData/LargeTable
             usage_data[:licensee] = license.licensee
             usage_data[:license_user_count] = license.restricted_user_count

ee/lib/gitlab/usage/metrics/instrumentations/historical_max_users_metric.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Usage
+    module Metrics
+      module Instrumentations
+        class HistoricalMaxUsersMetric < ::Gitlab::Usage::Metrics::Instrumentations::GenericMetric
+          value do
+            ::License.current.historical_max
+          end
+        end
+      end
+    end
+  end
+end

ee/spec/lib/ee/gitlab/usage_data_non_sql_metrics_spec.rb

@@ -15,7 +15,7 @@ RSpec.describe Gitlab::UsageDataNonSqlMetrics do
         described_class.uncached_data
       end
 
-      expect(recorder.count).to eq(54)
+      expect(recorder.count).to eq(55)
     end
   end
 end

ee/spec/lib/gitlab/usage/metrics/instrumentations/historical_max_users_metrics_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Usage::Metrics::Instrumentations::HistoricalMaxUsersMetric do
+  it_behaves_like 'a correct instrumented metric value', { time_frame: 'none', data_source: 'ruby' } do
+    let(:expected_value) { ::License.current.historical_max }
+  end
+end