Add pipeline_artifacts_size to ProjectStatistics

This new column will be used to count artifacts size
generated for pipeline artifacts by gitlab.

changelogs/unreleased/mo-add-pipeline-artifacts-size-to-project-statistics.yml

+---
+title: Add pipeline_artifacts_size to project_statistics
+merge_request: 39607
+author:
+type: added

db/migrate/20200817142800_add_pipeline_artifacts_size_to_project_statistics.rb

+# frozen_string_literal: true
+
+class AddPipelineArtifactsSizeToProjectStatistics < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    with_lock_retries do
+      add_column :project_statistics, :pipeline_artifacts_size, :bigint, default: 0, null: false
+    end
+  end
+
+  def down
+    with_lock_retries do
+      remove_column :project_statistics, :pipeline_artifacts_size, :bigint, default: 0, null: false
+    end
+  end
+end

db/schema_migrations/20200817142800

+b488cd2049300b293f584f193edc5435855f7bc85989648a3310dabc609d0af4
\ No newline at end of file

db/structure.sql

@@ -14556,7 +14556,8 @@ CREATE TABLE public.project_statistics (
     shared_runners_seconds_last_reset timestamp without time zone,
     packages_size bigint DEFAULT 0 NOT NULL,
     wiki_size bigint,
-    snippets_size bigint
+    snippets_size bigint,
+    pipeline_artifacts_size bigint DEFAULT 0 NOT NULL
 );
 
 CREATE SEQUENCE public.project_statistics_id_seq