Activates AWS Shield Advanced for an account.
shield_create_subscription()svc$create_subscription()
As part of this request you can specify EmergencySettings that
automaticaly grant the DDoS response team (DRT) needed permissions to
assist you during a suspected DDoS attack. For more information see
Authorize the DDoS Response Team to Create Rules and Web ACLs on Your Behalf.
When you initally create a subscription, your subscription is set to be
automatically renewed at the end of the existing subscription period.
You can change this by submitting an UpdateSubscription request.