title: Add a header when sending a message with php-enqueue and RabbitMQ
body: <p>I am trying to send a header using php-enqueue bundle
  I'm trying this:</p>
  <pre><code>public function __construct(
      ProducerInterface    $producer
  )
  {
      parent::__construct();
  
      $this-&gt;producer = $producer;
  }
  
  //... Inside function...
  $m = new Message(
     'message to send',
      [],
      [
         'm' =&gt; 1
      ]
  );
  
  $this-&gt;producer-&gt;sendCommand('newMessageFromApi', $m);
  </code></pre>
  <p>But the header does not reach the consumer.
  These are the only headers that arrive.</p>
  <pre><code>[
        &quot;content_type&quot; =&gt; &quot;text/plain&quot;,
        &quot;delivery_mode&quot; =&gt; 2,
        &quot;message_id&quot; =&gt; &quot;38f96af0-64de-4a31-9315-6b51dd5f8baf&quot;,
        &quot;timestamp&quot; =&gt; 1652027271
  ]
  </code></pre>