realm: Add setting to control adding "(guest)" indicator to name.

This commit adds new realm setting to control adding "(guest)"
indicator to names of guest users in the UI.

Fixes part of #26700.

web/src/server_events_dispatch.js

@@ -242,6 +242,7 @@ export function dispatch_normal_event(event) {
                 want_advertise_in_communities_directory: noop,
                 wildcard_mention_policy: noop,
                 enable_read_receipts: settings_account.update_send_read_receipts_tooltip,
+                enable_guest_user_indicator: noop,
             };
             switch (event.op) {
                 case "update":