Draft: sTGC raw data monitoring: jira ticket issue (ATLASRECTS-7645)

Follow up of the following jira ticket: https://its.cern.ch/jira/browse/ATLASRECTS-7645. Re-organization of the method fillsTgcEfficiencyHistograms in order to include only local definitions and use of std::array. Removal of 2D Efficiency plots from Expert folder in order to avoid duplication of plots.

Tagging: @carquin @jmaurer @amete

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