groups: Accept anonymous groups for can_access_all_users_group.

On the frontend, the selection is still a dropdown of system groups but
on the API level, we have started accepting anonymous groups similar to
other settings
We've kept require system groups true for now until we switch to group
picker on the frontend.

web/src/settings_components.ts

@@ -1044,6 +1044,7 @@ export function populate_data_for_realm_settings_request(
                 }
 
                 const realm_group_settings_using_new_api_format = new Set([
+                    "can_access_all_users_group",
                     "can_add_custom_emoji_group",
                     "can_create_groups",
                     "can_create_private_channel_group",