Add basic workflow endpoint with hello world message

[MAILPOET-4135]

mailpoet/lib/Automation/API/API.php

@@ -2,6 +2,7 @@
 
 namespace MailPoet\Automation\API;
 
+use MailPoet\Automation\API\Endpoints\WorkflowsEndpoint;
 use MailPoet\Automation\Exceptions\Exception;
 use MailPoet\Automation\WordPress;
 use ReflectionClass;
@@ -20,6 +21,7 @@ class API {
 
   /** @var array<string, class-string<Endpoint>> */
   private $routes = [
+    'workflows' => WorkflowsEndpoint::class,
   ];
 
   public function __construct(

mailpoet/lib/Automation/API/Endpoints/WorkflowsEndpoint.php

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

mailpoet/lib/DI/ContainerConfigurator.php

@@ -105,6 +105,7 @@ class ContainerConfigurator implements IContainerConfigurator {
     $container->autowire(\MailPoet\Automation\API\EndpointFactory::class)
       ->setPublic(true)
       ->setArgument('$container', new Reference(ContainerWrapper::class));
+    $container->autowire(\MailPoet\Automation\API\Endpoints\WorkflowsEndpoint::class)->setPublic(true);
     $container->autowire(\MailPoet\Automation\Automation::class)->setPublic(true);
     $container->autowire(\MailPoet\Automation\WordPress::class)->setPublic(true);
     // Config