Make prompt library icon in context panel staff-only for now (#12457)

This is still pretty raw, so I'd like to hold off on shipping it to all
users.

Release Notes:

- Hide the prompt library for non-staff until it is in a more complete
state.

crates/client/src/user.rs

@@ -192,10 +192,13 @@ impl UserStore {
 
                                 cx.update(|cx| {
                                     if let Some(info) = info {
-                                        cx.update_flags(info.staff, info.flags);
+                                        let disable_staff = std::env::var("ZED_DISABLE_STAFF")
+                                            .map_or(false, |v| v != "" && v != "0");
+                                        let staff = info.staff && !disable_staff;
+                                        cx.update_flags(staff, info.flags);
                                         client.telemetry.set_authenticated_user_info(
                                             Some(info.metrics_id.clone()),
-                                            info.staff,
+                                            staff,
                                         )
                                     }
                                 })?;