Add TriggerEvaluator

[zero88]

Is your feature request related to a problem? Please describe.
Extract the logic to check the trigger is able to run or stop by condition to TriggerEvaluator
That makes easier to inject custom check into scheduler API from the application side.

Describe the solution you'd like

• The Trigger Evaluator must be chained-able
• The interface should be

interface TriggerEvaluator {

   Future<TriggerContext> shouldRun(...);

   Future<TriggerContext> shouldStop(...);
}