Handle Wikipedia code blocks in /fetch command (#12780)

This PR extends the `/fetch` command with support for Wikipedia code
blocks.

Release Notes:

- N/A

crates/assistant/src/slash_command/fetch_command.rs

@@ -43,12 +43,15 @@ impl FetchSlashCommand {
             Box::new(markdown::ListHandler),
             Box::new(markdown::TableHandler::new()),
             Box::new(markdown::StyledTextHandler),
-            Box::new(markdown::CodeHandler),
         ];
         if url.contains("wikipedia.org") {
             use html_to_markdown::structure::wikipedia;
 
             handlers.push(Box::new(wikipedia::WikipediaChromeRemover));
+            handlers.push(Box::new(wikipedia::WikipediaInfoboxHandler));
+            handlers.push(Box::new(wikipedia::WikipediaCodeHandler::new()));
+        } else {
+            handlers.push(Box::new(markdown::CodeHandler));
         }
 
         convert_html_to_markdown(&body[..], handlers)