Add previewMediaType flag for simpler node preview rendering (#2694)

Co-authored-by: huchenlei <huchenlei@proton.me>

src/extensions/core/uploadAudio.ts

@@ -199,6 +199,8 @@ app.registerExtension({
         )
         uploadWidget.label = 'choose file to upload'
 
+        node.previewMediaType = 'audio'
+
         return { widget: uploadWidget }
       }
     }