Pseudo-stream version of JSON monitoring for 73X

This is an exact copy of PR#6095 intended to port the latter to 73X. The description of the original PR is copied below.
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This update to HLTrigger/JSONMonitoring switches to the pseudo-stream version and also adds some Level 1 trigger rate information. It requires the toJsonValue() function and thus also pulls in Srecko's changes to EventFilter/Utilities/interface/JsonMonitorable.h per his suggestion.