private void notifyConfigActivationListeners(ApplicationVersions applicationVersions) {
        hostRegistry.update(applicationVersions.getId(), applicationVersions.allHosts());
        configActivationListener.configActivated(applicationVersions);
    }
Gets a config for the given app, or null if not found
configserver/src/main/java/com/yahoo/vespa/config/server/application/TenantApplications.java