Add to CMSSW

[DryRun]

I had a chat Kenneth Long and Mariarosaria d'Alfonso, and it turns out Kenneth has been working on a more general project to add RecHit NanoAOD producers:

https://github.com/kdlong/cmssw/tree/pfNano_CMSSW_12_1_1
https://twiki.cern.ch/twiki/bin/viewauth/CMS/PfNanoAod

This opens a nice path to integrating HcalNano into CMSSW, where we will have a lot more central support, including configuration via cmsDriver instead of manual configs and perhaps even automatic workflows. Kenneth has already written an efficient HCAL RecHit producer, and we can copy over the digi/TP/etc producers.