Add counter to ParticleMassMonitor

Re-add counter to ParticleMassMonitor to know how many events have a mass within 1 mass sigma, that is defined by the user. The counter is used by the bremsstrahlung test Moore!2373 (merged).

Goes with Moore!2373 (merged), lhcb-datapkg/PRConfig!367 (merged)

FYI: @cmarinbe

Phys/ParticleMaker/src/ParticleMassMonitor.cpp

@@ -76,7 +76,7 @@ private:
   // Flag for tuple generation
   Gaudi::Property<bool> m_generateTuples{this, "GenerateTuples", false};
   // counters
-  mutable Gaudi::Accumulators::Counter<>           m_n1sigma{this, "Candidates in 1 sigma"};
+  mutable Gaudi::Accumulators::Counter<> m_n1sigma{this, "Candidates in 1 sigma"};
 
   // Daughter particles
   std::string m_daughter1;