Rename feature_category from usage_ping to service_ping

What does this MR do?

This MR aims to solve the issue #334303 (closed)

Changes

• Rename feature_category :usage_ping to :service_ping in:
  • lib/api/usage_data_non_sql_metrics.rb
  • lib/api/usage_data_queries.rb
  • lib/api/usage_data.rb
  • app/workers/gitlab_usage_ping_worker.rb
  • app/controllers/projects/service_ping_controller.rb
  • app/controllers/admin/application_settings_controller.rb
  • app/workers/all_queues.yml