Plot RoI map for the first leg only in multi-leg triggers [ATR-26626]

If we have a multipe-leg trigger, the monitoring RoI map should look at the first leg only, so that a HLT_eX_tauX chain would only produce an entry in the electron RoI map.

This fixes ATR-26626.

While the original problem (that the jet RoI map is non-empty) is rare, the fix should reduce the RoI multiplicity in a way that is noticeable even in few events, as suggested by @tamartin .
I have checked this on the AOD from 23.0/Athena/x86_64-centos7-gcc11-opt/2023-08-30T2101/TrigAnalysisTest/test_trigAna_RDOtoRun3DQ_v1Dev_build/ (20 events) and the RoI map event count reduced compared with the out-of-box test:
HLT_MuonsRoIs 640 -> 577
HLT_ElectronsRoIs: 659 -> 648

While this change is in no way urgent, it would be nice to have it in as soon as possible.

Tagging also @sshaw , @shanisch , @tnobe .

added 23.0 Trigger labels

This merge request affects 1 package:

• Trigger/TrigMonitoring/TrigHLTMonitoring

This merge request affects 1 file:

• Trigger/TrigMonitoring/TrigHLTMonitoring/src/TrigHLTMonitorAlgorithm.cxx

Adding @ebergeas as watcher

added DQ review-pending-level-1 labels

CI Result SUCCESS (hash 32fe8cb2)

	Athena
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cmake
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For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 77274]

Changes look fine from L1 perspective - Approving.

Cheers, Steffen (L1)

added review-approved label and removed review-pending-level-1 label

added frozen-tier0-violating label

removed frozen-tier0-violating label

added review-approved-tier0 label

resolved all threads

added review-approved-point1 label

merged

mentioned in commit 63ab32c5

mentioned in merge request !65545 (merged)