title: How to override default validation message of entity choice field?
body: <p>I have defined foreign key in my <code>User</code> entity:</p>
  
  <pre><code>/**
   * @ORM\ManyToOne(targetEntity="Region")
   */
  protected $region;
  </code></pre>
  
  <p>I'd like to use it in form as a choice field.</p>
  
  <pre><code>$builder-&gt;add('region');
  </code></pre>
  
  <p>Which works great in fact, until I want to validate if choice is valid entity id. In fact, that works great too, but I'm getting <code>This value is not valid</code> error message and I need to override / translate it and I have no idea how. It's some kind of automatic validation. Logically, I'd say it should be overridable if I set <code>@Assert\Choice...</code>, but even when I tried it with dummy values (<code>message="You shall not pass", choices={1,2}</code>), it seemed to ignore it completely.</p>