message: Add user agent to kudu client
diff: import { User } from 'azure-arm-website/lib/models';
  import { BasicAuthenticationCredentials } from 'ms-rest';
  +import { addExtensionUserAgent } from 'vscode-azureextensionui';
  import KuduClient from 'vscode-azurekudu';
  import { ArgumentError } from './errors';
  import { SiteClient } from './SiteClient';
  @@ -17,5 +18,7 @@ export async function getKuduClient(client: SiteClient): Promise<KuduClient> {
  const cred: BasicAuthenticationCredentials = new BasicAuthenticationCredentials(user.publishingUserName, user.publishingPassword);
  - return new KuduClient(cred, client.kuduUrl);
  + const kuduClient: KuduClient = new KuduClient(cred, client.kuduUrl);
  + addExtensionUserAgent(kuduClient);
  + return kuduClient;
  }
  