Add license_billable_users to Usage Ping for EE

ee/config/metrics/license/20210531204603_license_billable_users.yml

+---
+key_path: license_billable_users
+name: billable_users
+description: Count of all billable users (active users excluding bots and guests).
+product_section: growth
+product_stage: growth
+product_group: group::product intelligence
+product_category: collection
+value_type: string
+status: implemented
+milestone: "14.0"
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/62850
+time_frame: all
+data_source: database
+distribution:
+- ee
+tier:
+- premium
+- ultimate

ee/lib/ee/gitlab/usage_data.rb

@@ -97,6 +97,7 @@ module EE
             # rubocop: enable UsageData/LargeTable
             usage_data[:licensee] = license.licensee
             usage_data[:license_user_count] = license.restricted_user_count
+            usage_data[:license_billable_user_count] = license.daily_billable_users_count
             usage_data[:license_starts_at] = license.starts_at
             usage_data[:license_expires_at] = license.expires_at
             usage_data[:license_plan] = license.plan