Adds Compute Engine costs to the bq_billing query results (#1062)

* Adds GCE costs to bq_billing query results

We want to start alerting on significant changes to Compute Engine costs over
some number of days. This commit adds metrics for Compute Engine that we can
alert on.

* Adds missing comma to SQL in bq_billing.sql

config/federation/bigquery/bq_billing.sql

@@ -50,6 +50,12 @@ SELECT
   SUM(IF(period = "month" AND service = "BigQuery", cost, 0))/30 AS value_average_daily_bigquery,
   SUM(IF(period = "today" AND service = "BigQuery", cost, 0)) AS value_today_bigquery,
   SUM(IF(period = "yesterday" AND service = "BigQuery", cost, 0)) AS value_yesterday_bigquery,
-  SUM(IF(period = "before_yesterday" AND service = "BigQuery", cost, 0)) AS value_before_yesterday_bigquery
+  SUM(IF(period = "before_yesterday" AND service = "BigQuery", cost, 0)) AS value_before_yesterday_bigquery,
+  -- Compute Engine metrics.
+  SUM(IF(period = "month" AND service = "Compute Engine", cost, 0))/30 AS value_average_daily_gce,
+  SUM(IF(period = "today" AND service = "Compute Engine", cost, 0)) AS value_today_gce,
+  SUM(IF(period = "yesterday" AND service = "Compute Engine", cost, 0)) AS value_yesterday_gce,
+  SUM(IF(period = "before_yesterday" AND service = "Compute Engine", cost, 0)) AS value_before_yesterday_gce
 FROM
-  billing
+  billing
+