feat(spanner): update the API

#### spanner:v1

The following keys were added:
- schemas.UpdateDatabaseDdlMetadata.properties.throttled.description
- schemas.UpdateDatabaseDdlMetadata.properties.throttled.readOnly
- schemas.UpdateDatabaseDdlMetadata.properties.throttled.type

discovery/spanner-v1.json

@@ -1895,7 +1895,7 @@
       }
     }
   },
-  "revision": "20201107",
+  "revision": "20201130",
   "rootUrl": "https://spanner.googleapis.com/",
   "schemas": {
     "Backup": {
@@ -3628,6 +3628,11 @@
             "type": "string"
           },
           "type": "array"
+        },
+        "throttled": {
+          "description": "Output only. When true, indicates that the operation is throttled e.g due to resource constraints. When resources become available the operation will resume and this field will be false again.",
+          "readOnly": true,
+          "type": "boolean"
         }
       },
       "type": "object"

src/apis/spanner/v1.ts

@@ -1361,6 +1361,10 @@ export namespace spanner_v1 {
      * For an update this list contains all the statements. For an individual statement, this list contains only that statement.
      */
     statements?: string[] | null;
+    /**
+     * Output only. When true, indicates that the operation is throttled e.g due to resource constraints. When resources become available the operation will resume and this field will be false again.
+     */
+    throttled?: boolean | null;
   }
   /**
    * Enqueues the given DDL statements to be applied, in order but not necessarily all at once, to the database schema at some point (or points) in the future. The server checks that the statements are executable (syntactically valid, name tables that exist, etc.) before enqueueing them, but they may still fail upon later execution (e.g., if a statement from another batch of statements is applied first and it conflicts in some way, or if there is some data-related problem like a `NULL` value in a column to which `NOT NULL` would be added). If a statement fails, all subsequent statements in the batch are automatically cancelled. Each batch of statements is assigned a name which can be used with the Operations API to monitor progress. See the operation_id field for more details.