Add interface for workflow actions

[MAILPOET-4136]

mailpoet/lib/Automation/Engine/Workflows/Action.php

@@ -0,0 +1,11 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Automation\Engine\Workflows;
+
+interface Action {
+  public function getKey(): string;
+
+  public function getName(): string;
+
+  public function run(Workflow $workflow, WorkflowRun $workflowRun, Step $step): void;
+}