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/Cargo.toml

@@ -133,6 +133,8 @@ util.workspace = true
 uuid.workspace = true
 vim.workspace = true
 vim_mode_setting.workspace = true
+web_search.workspace = true
+web_search_providers.workspace = true
 welcome.workspace = true
 workspace.workspace = true
 zed_actions.workspace = true