Enable HLT prescaling tool for L1Decoder (ATR-20865)
The prescaling happens according to the HLTPrescaleSet. The HLTPrescalingSet is expected to always be there (job should be setup correctly), but if the HLTPrescaleSet is "empty" or doesn't contain certain chains, then the chains are activated (not prescaled) according to the property KeepUnknownChains
of the PrescalingTool which is True by default.
The desired behavior what to do in such case should be defined by operations at some point.