agent: Expose web search tool to beta users (#29273)

This gives all beta users access to the web search tool

Release Notes:

- agent: Added `web_search` tool

crates/web_search/src/web_search.rs

@@ -61,4 +61,11 @@ impl WebSearchRegistry {
             self.active_provider = Some(provider);
         }
     }
+
+    pub fn unregister_provider(&mut self, id: WebSearchProviderId) {
+        self.providers.remove(&id);
+        if self.active_provider.as_ref().map(|provider| provider.id()) == Some(id) {
+            self.active_provider = None;
+        }
+    }
 }