ResourceIdentifier: [required] The Amazon Resource Name (ARN) of the resource that the pending maintenance action applies to.
ApplyAction: [required] The pending maintenance action to apply to this resource.
Valid values: system-update, db-upgrade
OptInType: [required] A value that specifies the type of opt-in request or undoes an opt-in request. An opt-in request of type immediate can't be undone.
Valid values:
immediate - Apply the maintenance action immediately.
next-maintenance - Apply the maintenance action during the next maintenance window for the resource.
undo-opt-in - Cancel any existing next-maintenance opt-in requests.