[NanoAnalysis] Store best cand idx separately for the fiducial analysis

[namapane]

Add the index for the best candidate selected by Z1/Z2 so that the same production can be used for both the "regular" analysis and the fiducial one. This requires:

• adding indices for SR and CR: bestCandByZIdx, ZLLbest2P2FByZIdx, ZLLbest3P1FByZIdx, ZLLbestSIPCRByZIdx, ZLLbestSSByZIdx
• remove the parameter bestCandByMELA which would no longer be relevant.
• Handle the case where runMELA == False: ideally one would have to skip writing bestCandIdx and keep only bestCandByZIdx , but this would complicate things and possibly break scripts downstream that expect these variable, so probably the easiest thing is to set both variables with the byZ selection. (The same need to be done for the CR variables)
• Rework the "candidate suppression" for StoreOption.BestCandOnly: it would need to keep candidates belonging to both indices, if different
• Add the additional CR candidates if needed: it would be enough to add the proper selection here

Prior to this, it may be a good idea to revisit the need to have two different best candidate selection criteria.

• We should recheck how sub-optimal is the byZ criterion for associate production:"it was found to often pick the wrong set of leptons in leptonic ZH and WH events; we should check how often a candidate with a lepton not coming from the H is selected in case where all leptons from H are reconstructed.
• We may try to find better criteria that are based on kinematics that can be defined for the fiducial analysis so that they work in both cases.