Add support for "dynamic" triggers

[ezhulenev]

It would be great to be able to pass a function to "trigger" property, that will be called with slotId. Similar to what is available for oozieExternalService properties.

function deliverAbTrigger(slotId) {
  var scheduledTime = slotId.getScheduledTime();

  // If slot time after 8 AM: depend on same day DELIVER workflow
  // If slot time before 8 AM: depend on previous day DELIVER workflow
  var hour = scheduledTime.getHour();
  var deliverWorkflowShift = (hour >= 8) ? 8 - hour : -1 * hour - (24 - 8);

  // Define trigger based on slot scheduled time
  return offsetTrigger(
    deliverWorkflowShift,
    successTrigger(ID + "-" + DELIVER)
  )
}