chore: Update discovery artifacts (#1317)

## Discovery Artifact Change Summary:
contentv2[ [More details]](https://github.com/googleapis/google-api-python-client/commit/85dcfe41b40f6827345fadfcccfc78f31a872e4a)
contentv21[ [More details]](https://github.com/googleapis/google-api-python-client/commit/85dcfe41b40f6827345fadfcccfc78f31a872e4a)
dnsv1beta2[ [More details]](https://github.com/googleapis/google-api-python-client/commit/5dfd888f6af29ce3bd1589683cc22255acf971c5)
realtimebiddingv1alpha[ [More details]](https://github.com/googleapis/google-api-python-client/commit/26dc108c295c1d1ab93ee13bc70f4802c4d60d2d)
serviceconsumermanagementv1[ [More details]](https://github.com/googleapis/google-api-python-client/commit/736e39a686d43af2c49e3442066ec2cb78642792)
serviceconsumermanagementv1beta1[ [More details]](https://github.com/googleapis/google-api-python-client/commit/736e39a686d43af2c49e3442066ec2cb78642792)
servicemanagementv1[ [More details]](https://github.com/googleapis/google-api-python-client/commit/d34c2fed6e96f74b355a22c8a0fd2f0bf73898ec)
servicenetworkingv1[ [More details]](https://github.com/googleapis/google-api-python-client/commit/67d9d5d8392b86cb004dc340884227a42b2ff06f)
servicenetworkingv1beta[ [More details]](https://github.com/googleapis/google-api-python-client/commit/67d9d5d8392b86cb004dc340884227a42b2ff06f)
serviceusagev1[ [More details]](https://github.com/googleapis/google-api-python-client/commit/833c6db32348fc0c6e483710a0de4d5048c3fbae)
serviceusagev1beta1[ [More details]](https://github.com/googleapis/google-api-python-client/commit/833c6db32348fc0c6e483710a0de4d5048c3fbae)
diff --git a/googleapiclient/discovery_cache/documents/dns.v1.json b/googleapiclient/discovery_cache/documents/dns.v1.json
index d4880ba..af7ab2f 100644
--- a/googleapiclient/discovery_cache/documents/dns.v1.json
+++ b/googleapiclient/discovery_cache/documents/dns.v1.json
@@ -1245,7 +1245,7 @@
       }
     }
   },
-  "revision": "20210414",
+  "revision": "20210423",
   "rootUrl": "https://dns.googleapis.com/",
   "schemas": {
     "Change": {
@@ -1677,6 +1677,7 @@
         },
         "kind": {
           "default": "dns#managedZoneOperationsListResponse",
+          "description": "Type of resource.",
           "type": "string"
         },
         "nextPageToken": {