TrigCost: Add Rates Emulation Example

Add Rates Emulation example for phase-2 studies and fixes needed to run it:

• handle empty TDT in RatesAnalysisAlg
• handle empty xAODConfigSvc in RatesAnalysisAlg
• use cached ptr in RatesScanTrigger to fill the histogram

The example defines two electron triggers (including one threshold trigger):

// name, prescale, expressPrescale, seedName, seedPrescale, groups
ATH_CHECK(newTrigger("OFF_E10", 1, -1, "", 1, triggerGroup));

// name, thresholdMin, thresholdMax
ATH_CHECK(newScanTrigger("OFF_Ex", 20, 40));

Run with:

RatesEmulationExample.py Input.Files="['AOD.pool.root']" 2>&1 | tee emulation.log

Includes also follow up on !47764 (merged) - fix gethostname check @rbielski

@tamartin