Adds dependency_proxy_size to namespace statistics

For storing the total dependency proxy storage size at the namespace
level

Changelog: added

db/migrate/20220119141407_add_dependency_proxy_size_to_namespace_statistics.rb

+# frozen_string_literal: true
+
+class AddDependencyProxySizeToNamespaceStatistics < Gitlab::Database::Migration[1.0]
+  def change
+    add_column :namespace_statistics, :dependency_proxy_size, :bigint, default: 0, null: false
+  end
+end

db/schema_migrations/20220119141407

+18b3ef459c3633ebd4b418b4436d3d50b0dc697fa7c4ef4d2e1f62b01d656bce
\ No newline at end of file

db/structure.sql

@@ -16541,7 +16541,8 @@ CREATE TABLE namespace_statistics (
     shared_runners_seconds integer DEFAULT 0 NOT NULL,
     shared_runners_seconds_last_reset timestamp without time zone,
     storage_size bigint DEFAULT 0 NOT NULL,
-    wiki_size bigint DEFAULT 0 NOT NULL
+    wiki_size bigint DEFAULT 0 NOT NULL,
+    dependency_proxy_size bigint DEFAULT 0 NOT NULL
 );
 
 CREATE SEQUENCE namespace_statistics_id_seq