title: Custom nested form type easyadmin
body: <p>I have an entity <em>User</em> and an entity <em>Address</em> which are in <strong>OneToOne</strong> relationship. I would like to display the address type in the User Crud in EasyAdmin, and I don't find a way to do just like Symfony <code>-&gt;add('address', AddressType::class)</code>.
  I tried the following options:</p>
  <pre><code>CollectionField::new('address')
              -&gt;setEntryIsComplex(true)
              -&gt;setEntryType(AddressType::class)
              -&gt;setFormTypeOptions([
                  'by_reference' =&gt; false,
                  'required' =&gt; true
              ]),
  </code></pre>
  <p>But this makes the user able to add as many as addresses he wants, although I just want one.</p>
  <pre><code>AssociationField::new('address')-&gt;hideOnIndex()
  </code></pre>
  <p>This one makes the user choose an existing address in a list. That's not an embed of a form type.</p>
  <p>Does anyone have an idea?</p>