title: check if an email id exists in the AdminDirectory.Users
body: <p>Is there way to check if an email id exists in the AdminDirectory.Users or not? I know that <a href="https://developers.google.com/admin-sdk/directory/v1/reference/users/get" rel="nofollow noreferrer">https://developers.google.com/admin-sdk/directory/v1/reference/users/get</a> retrieves all the users, is there a query like <code>exists</code>(from sql) in Google apps script?</p>