title: symfony 4 form with multiple arrayCollection
body: <p>well, every user has multiple sports so i have created table users and table sports and table usersport</p>
  
  <p>so i want that the user select multiple sport and store it in table user sport </p>
  
  <pre><code>user entity arrayCollection
  /**
   * @ORM\OneToMany(targetEntity="SportUser", mappedBy="user")
   */
  private $sports;
  public function __construct()
  {       
      $this-&gt;sports = new ArrayCollection();
  }
  </code></pre>
  
  <p>//usertype </p>
  
  <pre><code>-&gt;add('sports', CollectionType::class, [
  'entry_type'    =&gt; SportType::class,
      'allow_add'     =&gt; true,
      'allow_delete'  =&gt; true,
   ]) 
  </code></pre>
  
  <p>i want to make a user form with multi-select from entity sport and store it in table user sport </p>