Leave on-save email validation only in SubscriberSaveController

[MAILPOET-5878]

mailpoet/lib/Doctrine/EntityTraits/ValidationGroupsTrait.php

@@ -0,0 +1,18 @@
+<?php declare(strict_types = 1);
+
+namespace MailPoet\Doctrine\EntityTraits;
+
+trait ValidationGroupsTrait {
+  /**
+   * @var array|null
+   */
+  private $validationGroups;
+
+  public function getValidationGroups(): ?array {
+    return $this->validationGroups;
+  }
+
+  public function setValidationGroups(?array $validationGroups): void {
+    $this->validationGroups = $validationGroups;
+  }
+}