Update output message in pflow muon linking and update trigger monitoring from AOD workflow

Tweak error message output to correctly state the problem. Set CA production step to Derivation in monitoring from AOD workflow. This is needed to correctly configure the pflow-muon linking when running from AOD, which autoconfigure based on the ProductionStep value. For discussion: Its a bit hacky to use Derivation. OTOH there is no relevant ProductionStep value in the CA enum for this workflow...so either we just use Derivation for all "from AOD" workflows or we add new enum values (how many might this end up being? Perhaps fine if 1, if 10-20 for all possible workflows perhaps it's not desirable given only PFlowMuon linking needs to check this in "from AOD" workflows for its auto configuration?) Tagging @martindl who reported the trigger issue. @christos what do you think?