Import of the developments in TrigMuonMonitoring for the 2018 HI runs

Description

The developments in the muon trigger monitoring for the 2018 HI runs were somehow not merged into master in the pseudomerge process. This MR contains these updates. The change were made on top of master of clean atlas/athena (not atlas/athenaprivate1) by applying the patch of the last three commits of 21.0-2018hi-dev, which was merged in !15213. This procedure follows the instruction, https://twiki.cern.ch/twiki/bin/viewauth/AtlasComputing/OpeningTheSoftware. The commits and the changes in the bottom of this page are quite reasonable.

Validation

It was confirmed that the compilation with Athena,master,latest(2019-01-19T2257) was successfull.

Approval

@markowen, @nakahama, @morgens, @rbielski, please tell if we need more tests or there are something unclear.

JIRA

Please post comments in ATR-19014.