add ability to specify onLinkTap for url attachments

packages/stream_chat_flutter/lib/src/attachment/url_attachment.dart

@@ -14,6 +14,7 @@ class UrlAttachment extends StatelessWidget {
       horizontal: 16,
       vertical: 8,
     ),
+    this.onLinkTap,
   }) : super(key: key);
 
   /// Attachment to be displayed
@@ -28,13 +29,20 @@ class UrlAttachment extends StatelessWidget {
   /// [MessageThemeData] for showing image title
   final MessageThemeData messageTheme;
 
+  /// The function called when tapping on a link
+  final void Function(String)? onLinkTap;
+
   @override
   Widget build(BuildContext context) {
     final chatThemeData = StreamChatTheme.of(context);
     return GestureDetector(
       onTap: () {
         final titleLink = urlAttachment.titleLink;
-        if (titleLink != null) launchURL(context, titleLink);
+        if (titleLink != null) {
+          onLinkTap != null
+              ? onLinkTap!(titleLink)
+              : launchURL(context, titleLink);
+        }
       },
       child: Column(
         crossAxisAlignment: CrossAxisAlignment.stretch,

packages/stream_chat_flutter/lib/src/message_widget.dart

@@ -1013,6 +1013,7 @@ class _MessageWidgetState extends State<MessageWidget>
       hostDisplayName: hostDisplayName,
       textPadding: widget.textPadding,
       messageTheme: widget.messageTheme,
+      onLinkTap: widget.onLinkTap,
     );
   }