AthenaKernel+StoreGate: Add key argument to IProxyDict::sourceID.
Add an argument to IProxyDict::sourceID to specify a non-default key for the DataHeader. To be used to clean up DoubleEventSelectorAthenaPool.
Add an argument to IProxyDict::sourceID to specify a non-default key for the DataHeader. To be used to clean up DoubleEventSelectorAthenaPool.