def find_or_create_subscription(key, subscription_params = {})
      subscription = find_subscription(key)
      subscription || create_subscription(subscription_params.merge(key: key))
    end
def find_or_create_subscription(key, subscription_params = {})
      subscription = find_subscription(key)
      subscription || create_subscription(subscription_params.merge(key: key))
    end
Gets subscription of the target and notification key.

 @param [Hash] key                 Key of the notification for subscription
 @param [Hash] subscription_params Parameters to create subscription record
 @return [Subscription] Found or created subscription instance