agent: Add websearch tool (#28621)

Staff only for now. We'll work on making this usable for non zed.dev
users later

Release Notes:

- N/A

---------

Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Danilo Leal <daniloleal09@gmail.com>
Co-authored-by: Marshall Bowers <git@maxdeviant.com>

crates/feature_flags/src/feature_flags.rs

@@ -84,6 +84,11 @@ impl FeatureFlag for ZedPro {
     const NAME: &'static str = "zed-pro";
 }
 
+pub struct ZedProWebSearchTool {}
+impl FeatureFlag for ZedProWebSearchTool {
+    const NAME: &'static str = "zed-pro-web-search-tool";
+}
+
 pub struct NotebookFeatureFlag;
 
 impl FeatureFlag for NotebookFeatureFlag {