TrigServices: Benchmark and improve TrigMessageSvc monitoring speed

I was going through some VTune results and noticed this call was fairly high (for such a basic service) on the hotspots list. From the benchmark included here it seems that adding the check preventing unnecessary LabelsDeflate (inspired by the AthenaMonitoringKernel solution) speeds up messaging by a factor of 2. The 50k messages from 1k sources take around 4.2 seconds on my system without the if-statement and around 2.0 seconds after adding it, when printing to stdout. If stdout is redirected to file, the difference is 3.2 seconds vs 1.2 seconds.

The benchmark is added as a unit test.