Online jet monitoring: always require >=1 jet trigger to fire to fill plots

This MR addresses ATR-22548, adding the requirement of at least any one jet trigger in an event to fire during online monitoring of jets where no specific trigger/chain selection is applied. This avoids filling the corresponding "NoTriggerSelection" plots multiple times as a result of triggers of other related signatures (MET, bjets) firing.

Also adding an example of a recent MR to illustrate usage of a multi-SelectSpec.

Tagging @jbossios