Add storage service for workflows & create workflow method

[MAILPOET-4136]

mailpoet/lib/Automation/Engine/Storage/WorkflowStorage.php

@@ -0,0 +1,29 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Automation\Engine\Storage;
+
+use MailPoet\Automation\Engine\Exceptions;
+use MailPoet\Automation\Engine\Workflows\Workflow;
+use wpdb;
+
+class WorkflowStorage {
+  /** @var string */
+  private $table;
+
+  /** @var wpdb */
+  private $wpdb;
+
+  public function __construct() {
+    global $wpdb;
+    $this->table = $wpdb->prefix . 'mailpoet_automation_workflows';
+    $this->wpdb = $wpdb;
+  }
+
+  public function createWorkflow(Workflow $workflow): int {
+    $result = $this->wpdb->insert($this->table, $workflow->toArray());
+    if (!$result) {
+      throw Exceptions::databaseError($this->wpdb->last_error);
+    }
+    return $this->wpdb->insert_id;
+  }
+}