public ConfigChangeActions getConfigChangeActions() {
            return new ConfigChangeActions(results.stream().map(result -> result.actions)
                                                           .flatMap(Collection::stream)
                                                           .toList());
         }
Collects the config change actions from all model factory creations and returns the union of these actions.
A system in the process of upgrading Vespa will have hosts running both version X and Y, and this will change
during the upgrade process. Trying to be smart about which actions to perform on which hosts depending
on the version running will be a nightmare to maintain. A pragmatic approach is therefore to just use the
union of all actions as this will give the correct end result at the cost of perhaps restarting nodes twice
(once for the upgrading case and once for a potential restart action).
configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionPreparer.java