Possibility to more easily use the UniqueIDGenSvc with Functional algorithms

[tmadlener]

Currently our UniqueIDGenSvc is already working with the Functional algorithms, but it requires a bit of setup to get there. I think in some cases this also makes it necessary to change the flavor of the functional, e.g. (as will become apparent soon), it's not possible to have a Producer, instead one would need a Transformer.

What is possible at the moment is this

class UniqueIDGenSvcTransfomer final
    : k4FWCore::Transformer<podio::UserDataCollection<int64_t>(const edm4hep::EventHeaderCollection&)> {
public:
  UniqueIDGenSvcTransfomer(const std::string& name, ISvcLocator* svcLoc)
      : Transformer(name, svcLoc, {KeyValues("EventHeaderCollection", {"EventHeader"})},
                    {KeyValues("OutputCollection", {"seeds"})}) {}

  StatusCode initialize() final {
    m_uniqueIDSvc = serviceLocator()->service("UniqueIDGenSvc");
    return StatusCode::SUCCESS;
  }

  podio::UserDataCollection<int64_t> operator()(const edm4hep::EventHeaderCollection& evtHeader) const final {
    // we need the event header here to get to the event and run number.
    const auto evt = evtHeader[0];
    auto       uid = m_uniqueIDSvc->getUniqueID(evt.getEventNumber(), evt.getRunNumber(), name());

    auto coll = podio::UserDataCollection<int64_t>();
    coll.push_back(uid);
    return coll;
  }

private:
  SmartIF<IUniqueIDGenSvc> m_uniqueIDSvc{nullptr};
};

I am wondering if it's possible to make this a bit cleaner, i.e. such that getUniqueID() could be done without arguments in which case it would just get the event and run number from somewhere (potentially another service?).