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/zed/src/main.rs

@@ -490,6 +490,8 @@ fn main() {
             app_state.fs.clone(),
             cx,
         );
+        web_search::init(cx);
+        web_search_providers::init(app_state.client.clone(), cx);
         snippet_provider::init(cx);
         inline_completion_registry::init(
             app_state.client.clone(),