feat: 919 - new field KnowledgePanelImageElement.link_url

Impacted files:
* `knowledge_panel_element.dart`: added the `'link_url'` field; fixed the tag for `'alt'` field
* `knowledge_panel_element.g.dart`: generated
* `user.g.dart`: generated - I guess the latest changes in `user.dart` were not followed by `dart run build_runner build`

lib/src/model/knowledge_panel_element.dart

@@ -95,11 +95,15 @@ class KnowledgePanelImageElement extends JsonObject {
   final int? height;
 
   /// Alt Text of the image.
-  @JsonKey(name: 'alt_text')
+  @JsonKey(name: 'alt')
   final String? altText;
 
+  /// URL, for clickable image.
+  @JsonKey(name: 'link_url')
+  final String? linkUrl;
+
   const KnowledgePanelImageElement(
-      {required this.url, this.width, this.height, this.altText});
+      {required this.url, this.width, this.height, this.altText, this.linkUrl});
 
   factory KnowledgePanelImageElement.fromJson(Map<String, dynamic> json) =>
       _$KnowledgePanelImageElementFromJson(json);