Migrate existing endpoints to the new structure

[MAILPOET-4207]

mailpoet/lib/Automation/Engine/Endpoints/Workflows/WorkflowsGetEndpoint.php

@@ -0,0 +1,13 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Automation\Engine\Endpoints\Workflows;
+
+use MailPoet\Automation\Engine\API\Endpoint;
+use MailPoet\Automation\Engine\API\Request;
+use MailPoet\Automation\Engine\API\Response;
+
+class WorkflowsGetEndpoint extends Endpoint {
+  public function handle(Request $request): Response {
+    return new Response(['message' => 'Hello world.']);
+  }
+}