Add HGCal graph NN producers

[kpedro88]

The HGCal graph NN-based reconstruction has not been officially introduced in CMSSW. Implementation in a SonicTriton producer is likely the easiest path (especially for a PyTorch graph-based network, since the PyTorch C++ API is not yet available in CMSSW). There are multiple networks to implement, including edge classification (for clustering) and dynamic reduction (for energy regression etc.).

Particular considerations:

• Consider introducing ProcessModifier to enable the alternative sequence

Assigned to: @tklijnsma, @lgray

[kpedro88]

Relevant: https://github.com/lgray/triton-torchgeo-gat-example