Convenience overload to get CellIDEncoding more easily

Currently it's necessary to do something like

```cpp
auto cellIDEncoding = k4FWCore::getParameter<std::string>(podio::collMetadataParamName("collection-name", "CellIDEncoding"));
```

I think given the wide use of cell id encodings we should make it easier to do this such that users don't have to know about all the bits and pieces that go into how we encode "collection parameters".