Resolve #3469273 "Add event for scheduler finish"

Closes #3469273

src/Event/SchedulerFinish.php

+<?php
+
+namespace Drupal\scheduler\Event;
+
+use Drupal\Component\EventDispatcher\Event;
+
+/**
+ * Scheduler base event for finish.
+ */
+class SchedulerFinish extends Event {
+
+  /**
+   * Flag for finish.
+   *
+   * @var bool
+   */
+  public $finish;
+
+  /**
+   * Scheduler finish constructor.
+   *
+   * @param int $finish
+   *   Scheduler Finish.
+   */
+  public function __construct($finish = TRUE) {
+    $this->finish = $finish;
+  }
+
+}