Disable /search by default (#20252)

This stops us sending GetCachedEmbeddings requests which frequently time
out
after 10s, and block the collab connection.

Release Notes:

- N/A

crates/assistant/src/slash_command/search_command.rs

@@ -21,6 +21,10 @@ pub(crate) struct SearchSlashCommandFeatureFlag;
 
 impl FeatureFlag for SearchSlashCommandFeatureFlag {
     const NAME: &'static str = "search-slash-command";
+
+    fn enabled_for_staff() -> bool {
+        false
+    }
 }
 
 pub(crate) struct SearchSlashCommand;