feat(bigquery): update the API

#### bigquery:v2

The following keys were added:
- schemas.JobStatistics2.properties.ddlDestinationTable.$ref
- schemas.JobStatistics2.properties.ddlDestinationTable.description

discovery/bigquery-v2.json

@@ -1683,7 +1683,7 @@
       }
     }
   },
-  "revision": "20210422",
+  "revision": "20210515",
   "rootUrl": "https://bigquery.googleapis.com/",
   "schemas": {
     "AggregateClassificationMetrics": {
@@ -4096,6 +4096,10 @@
           "format": "int64",
           "type": "string"
         },
+        "ddlDestinationTable": {
+          "$ref": "TableReference",
+          "description": "[Output-only] The DDL destination table. Present only for ALTER TABLE RENAME TO queries. Note that ddl_target_table is used just for its type information."
+        },
         "ddlOperationPerformed": {
           "description": "The DDL operation performed, possibly dependent on the pre-existence of the DDL target. Possible values (new values might be added in the future): \"CREATE\": The query created the DDL target. \"SKIP\": No-op. Example cases: the query is CREATE TABLE IF NOT EXISTS while the table already exists, or the query is DROP TABLE IF EXISTS while the table does not exist. \"REPLACE\": The query replaced the DDL target. Example case: the query is CREATE OR REPLACE TABLE, and the table already exists. \"DROP\": The query deleted the DDL target.",
           "type": "string"

src/apis/bigquery/v2.ts

@@ -1801,6 +1801,10 @@ export namespace bigquery_v2 {
      * [Output-only] [Preview] The number of row access policies affected by a DDL statement. Present only for DROP ALL ROW ACCESS POLICIES queries.
      */
     ddlAffectedRowAccessPolicyCount?: string | null;
+    /**
+     * [Output-only] The DDL destination table. Present only for ALTER TABLE RENAME TO queries. Note that ddl_target_table is used just for its type information.
+     */
+    ddlDestinationTable?: Schema$TableReference;
     /**
      * The DDL operation performed, possibly dependent on the pre-existence of the DDL target. Possible values (new values might be added in the future): "CREATE": The query created the DDL target. "SKIP": No-op. Example cases: the query is CREATE TABLE IF NOT EXISTS while the table already exists, or the query is DROP TABLE IF EXISTS while the table does not exist. "REPLACE": The query replaced the DDL target. Example case: the query is CREATE OR REPLACE TABLE, and the table already exists. "DROP": The query deleted the DDL target.
      */