access `rule` inside `compact.group` function

[vsnig]

To be consistent with other functions that we pass to rules (toUpdateRequest etc.) that have signature (uow, rule) => ... can we have similar signature for compact.group function? Changing this:

    .group(rule.compact.group || ((uow) => uow.event.partitionKey))

to this:

    .group((uow) => rule.compact.group(uow, rule) || ((uow) => uow.event.partitionKey))