migrate code in CaloFuture to Digits v2, Clusters v2

Adopt to the new Digits v2 and Clusters v2 introduced in LHCb!2166 (merged)

To be backwards compatible, CaloFutureShowerOverlap, which used to copy its input to a new output, now takes the v2 Clusters as input, and instead of just copying, it converts to the 'old' clusters. As a result, all existing consumers of clusters downstream of CaloFutureShowerOverlap are OK.

In addition, there are also direct consumers of digits, which have been converted as well: CaloFutureTrack2IDAlg, CaloFutureEnergyForTrack, FutureNeutralIDTool, FutureGammaPi0XGBoostTool, FutureGammaPi0SeparationTool, CaloFutureHypo2CaloFuture, CaloFuture2CaloFuture, CaloFutureEFlowBase and CaloFutureDigitMonitor.