feat: Add support for dynamic thumbnails in Artplayer

The code changes introduce a new `art.thumbnails` property that allows for dynamic setting of thumbnails in Artplayer. This feature enhances the user experience by providing a visual preview of the video content.

packages/artplayer/src/control/index.js

@@ -81,15 +81,13 @@ export default class Control extends Component {
             );
         }
 
-        if (option.thumbnails.url && !option.isLive) {
-            this.add(
-                thumbnails({
-                    name: 'thumbnails',
-                    position: 'top',
-                    index: 20,
-                }),
-            );
-        }
+        this.add(
+            thumbnails({
+                name: 'thumbnails',
+                position: 'top',
+                index: 20,
+            }),
+        );
 
         this.add(
             playAndPause({