Feature: Access possible options for string inputs #291
Description
Dear Correctionlib authors
Currently there doesn't seem to be a mechanism for finding the possible options for string inputs. This would be quite helpful as for instance Muon SFs are currently provided with the central SF as "sf" in Run 2, but "nominal" in Run 3, and the descriptions of the inputs are not always clear, particularly regarding the names of systematic uncertainties, which vary between POGs. Would it be possible to provide a list of accepted keys, please?