def unsubscribe_to_optional_target(optional_target_name, options = {})
      unsubscribed_at = options[:unsubscribed_at] || Time.current
      update(optional_targets: optional_targets.merge(
        Subscription.to_optional_target_key(optional_target_name) => false,
        Subscription.to_optional_target_unsubscribed_at_key(optional_target_name) => unsubscribed_at)
      )
    end
def unsubscribe_to_optional_target(optional_target_name, options = {})
      unsubscribed_at = options[:unsubscribed_at] || Time.current
      update(optional_targets: optional_targets.merge(
        Subscription.to_optional_target_key(optional_target_name) => false,
        Subscription.to_optional_target_unsubscribed_at_key(optional_target_name) => unsubscribed_at)
      )
    end
Unsubscribes to the specified optional target.

 @param [String, Symbol] optional_target_name Class name of the optional target implementation (e.g. :amazon_sns, :slack)
 @param [Hash]           options              Options for unsubscribing to the specified optional target
 @option options [DateTime] :unsubscribed_at (Time.current) Time to set to unsubscribed_[optional_target_name]_at in optional_targets hash of the subscription record
 @return [Boolean] If successfully updated subscription instance