Get TrigEventSelectionAlg working in AthAnalysis

This is a "fix" for an issue I was getting running a few algorithms that used CutFlowSvc in AthAnalysis.

On the first event I get

CutFlowSvc                                          ERROR Inconsistent weights and variation sizes 217 and 1
terminate called after throwing an instance of 'std::runtime_error'
  what():  Inconsistent weights and variation sizes

I'm tagging @tadej, @khoo, @jburr, @frenner, @viruelas. I'll work on an MRE, for now the problem is demonstrated in some analysis code.

Roughly speaking, I set up MainServicesConfig, SystematicsSvc, TrigDecisionTool, TrigEventSelectionAlg, and call makeEventSelectionAnalysisSequence.

Does anyone have this working in AthAnalysis?