private Bcp complete(Bcp bcp, List<Step> steps) {
        if ( ! bcp.groups().isEmpty()) return bcp; // has explicit groups
        var group = new Bcp.Group(prodRegions(steps).stream().map(region -> new Bcp.RegionMember(region, 1.0)).toList(),
                                  bcp.defaultDeadline().orElse(Duration.ZERO));
        return bcp.withGroups(List.of(group));
    }
A bcp instance as written and imported may either specify groups containing all regions,
or no groups, meaning it should contain one group with all regions.
This adds that missing implicit group when appropriate.
config-model-api/src/main/java/com/yahoo/config/application/api/xml/DeploymentSpecXmlReader.java