Add missing usage_ping_enabled to API settings

Identified while resolving conflicts in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/5906

lib/api/settings.rb

@@ -129,6 +129,7 @@ module API
       optional :gitaly_timeout_default, type: Integer, desc: 'Default Gitaly timeout, in seconds. Set to 0 to disable timeouts.'
       optional :gitaly_timeout_medium, type: Integer, desc: 'Medium Gitaly timeout, in seconds. Set to 0 to disable timeouts.'
       optional :gitaly_timeout_fast, type: Integer, desc: 'Gitaly fast operation timeout, in seconds. Set to 0 to disable timeouts.'
+      optional :usage_ping_enabled, type: Boolean, desc: 'Every week GitLab will report license usage back to GitLab, Inc.'
 
       ApplicationSetting::SUPPORTED_KEY_TYPES.each do |type|
         optional :"#{type}_key_restriction",