[Phase-2] Requesting addition of sum type for HT/MHT sums producers

[artlbv]

I would like to request the addition of the type of sum identifier to the Phase-2 sums objects, i.e. Correlator, Calo and TK sums (where applicable).

The main goal is that one could identify the type of sum, e.g. HT, MHT, etc (probably more to come?) via a dedicated identifier a la phase-1. Currently one has to know at which index which sum is.

@EmyrClement @pallabidas @thesps @gpetruc @BenjaminRS
Could you comment on whether this would be feasible?

IMO this could also make the P2GT menu/producer simpler with less hard-coding if eventually more sums are needed (e.g. ML MET/HT etc) @HaarigerHarald @qvyz.

fyi @aloeliger @epalencia -> this is not a request to you, but I find this place the best to place it.
let me know if you think otherwise!