Move automation engine code under "Engine" namespace

This is to separate the engine itself from "integrations" that will be
built on top of the engine.

[MAILPOET-4136]

mailpoet/lib/Automation/Engine/API/Endpoints/SystemDatabaseEndpoint.php

@@ -0,0 +1,38 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Automation\Engine\API\Endpoints;
+
+use MailPoet\Automation\Engine\API\Endpoint;
+use MailPoet\Automation\Engine\API\Request;
+use MailPoet\Automation\Engine\API\Response;
+use MailPoet\Automation\Engine\Migrations\Migrator;
+use MailPoet\Features\FeatureFlagsController;
+use MailPoet\Features\FeaturesController;
+
+class SystemDatabaseEndpoint extends Endpoint {
+  /** @var FeatureFlagsController */
+  private $featureFlagsController;
+
+  /** @var Migrator */
+  private $migrator;
+
+  public function __construct(
+    FeatureFlagsController $featureFlagsController,
+    Migrator $migrator
+  ) {
+    $this->migrator = $migrator;
+    $this->featureFlagsController = $featureFlagsController;
+  }
+
+  public function post(Request $request): Response {
+    $this->migrator->deleteSchema();
+    $this->migrator->createSchema();
+    return new Response(null);
+  }
+
+  public function delete(Request $request): Response {
+    $this->migrator->deleteSchema();
+    $this->featureFlagsController->set(FeaturesController::AUTOMATION, false);
+    return new Response(null);
+  }
+}