feat(dns): update the API

#### dns:v1beta2

The following keys were added:
- schemas.Quota.properties.gkeClustersPerResponsePolicy.description
- schemas.Quota.properties.gkeClustersPerResponsePolicy.format
- schemas.Quota.properties.gkeClustersPerResponsePolicy.type

discovery/dns-v1beta2.json

@@ -1740,7 +1740,7 @@
       }
     }
   },
-  "revision": "20210423",
+  "revision": "20210513",
   "rootUrl": "https://dns.googleapis.com/",
   "schemas": {
     "Change": {
@@ -2611,6 +2611,11 @@
           "format": "int32",
           "type": "integer"
         },
+        "gkeClustersPerResponsePolicy": {
+          "description": "Maximum allowed number of GKE clusters per response policy.",
+          "format": "int32",
+          "type": "integer"
+        },
         "kind": {
           "default": "dns#quota",
           "type": "string"

src/apis/dns/v1beta2.ts

@@ -653,6 +653,10 @@ export namespace dns_v1beta2 {
      * Maximum allowed number of GKE clusters to which a privately scoped zone can be attached.
      */
     gkeClustersPerManagedZone?: number | null;
+    /**
+     * Maximum allowed number of GKE clusters per response policy.
+     */
+    gkeClustersPerResponsePolicy?: number | null;
     kind?: string | null;
     /**
      * Maximum allowed number of managed zones in the project.