[Embed] Use new attachment route format

plugins/Embed/templates/embed/embedView.html.twig

@@ -3,8 +3,7 @@
         {% if attributes['has_attachment'] != false %}
             {% set thumbnail_parameters = {
                 'id': embed.getAttachmentId(),
-                'w': attributes['width'],
-                'h': attributes['height']
+                'size': 'small'
             } %}
             <img alt="{{embed.getTitle() | escape}}" class="{{attributes['class']}}"
                  width="{{attributes['width']}}" height="{{attributes['height']}}"
@@ -37,4 +36,4 @@
     <div class="p-summary embed">
         {{ embed.getDescription() | escape }}
     </div>
-</article>
+</article>