Record db table sizes in datadog where we can use them to generate relevant alerts (#5377)

lib/tasks/fetch.rake

@@ -123,5 +123,8 @@ task record_db_table_counts: :environment do
         table_size: estimate,
       }
     )
+    DataDogStatsClient.gauge(
+      "postgres.db_table_size", estimate, tags: { table_name: table_name }
+    )
   end
 end