private ArrayList<Integer> sortSetIntoList(Set<Integer> set) {
        var sortedList = new ArrayList<>(set);
        Collections.sort(sortedList);
        return sortedList;
    }
Returns an optional Result, where return value is:
- No wanted state for other nodes, return Optional.empty
- Wanted state for nodes/groups are not UP:
- if less than maxNumberOfGroupsAllowedToBeDown: return Optional.of(allowed)
     else: if node is in group with nodes already down: return Optional.of(allowed), else Optional.of(disallowed)
clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/NodeStateChangeChecker.java