feat(dataflow): update the API

#### dataflow:v1b3

The following keys were added:
- schemas.FlexTemplateRuntimeEnvironment.properties.stagingLocation.description
- schemas.FlexTemplateRuntimeEnvironment.properties.stagingLocation.type

The following keys were changed:
- auth.oauth2.scopes.https://www.googleapis.com/auth/userinfo.email.description

discovery/dataflow-v1b3.json

@@ -12,7 +12,7 @@
           "description": "View your Google Compute Engine resources"
         },
         "https://www.googleapis.com/auth/userinfo.email": {
-          "description": "View your email address"
+          "description": "See your primary Google Account email address"
         }
       }
     }
@@ -2225,7 +2225,7 @@
       }
     }
   },
-  "revision": "20210331",
+  "revision": "20210408",
   "rootUrl": "https://dataflow.googleapis.com/",
   "schemas": {
     "ApproximateProgress": {
@@ -3372,6 +3372,10 @@
           "description": "The email address of the service account to run the job as.",
           "type": "string"
         },
+        "stagingLocation": {
+          "description": "The Cloud Storage path for staging local files. Must be a valid Cloud Storage URL, beginning with `gs://`.",
+          "type": "string"
+        },
         "subnetwork": {
           "description": "Subnetwork to which VMs will be assigned, if desired. You can specify a subnetwork using either a complete URL or an abbreviated path. Expected to be of the form \"https://www.googleapis.com/compute/v1/projects/HOST_PROJECT_ID/regions/REGION/subnetworks/SUBNETWORK\" or \"regions/REGION/subnetworks/SUBNETWORK\". If the subnetwork is located in a Shared VPC network, you must use the complete URL.",
           "type": "string"

src/apis/dataflow/v1b3.ts

@@ -918,6 +918,10 @@ export namespace dataflow_v1b3 {
      * The email address of the service account to run the job as.
      */
     serviceAccountEmail?: string | null;
+    /**
+     * The Cloud Storage path for staging local files. Must be a valid Cloud Storage URL, beginning with `gs://`.
+     */
+    stagingLocation?: string | null;
     /**
      * Subnetwork to which VMs will be assigned, if desired. You can specify a subnetwork using either a complete URL or an abbreviated path. Expected to be of the form "https://www.googleapis.com/compute/v1/projects/HOST_PROJECT_ID/regions/REGION/subnetworks/SUBNETWORK" or "regions/REGION/subnetworks/SUBNETWORK". If the subnetwork is located in a Shared VPC network, you must use the complete URL.
      */