TrigCostMonitor: migrate Modifiers to flags

Replace the following Modifiers:

• enableCostMonitoring was enabled by default. Instead set the corresponding flag to True.
• forceCostMonitoring is replaced by setting the relevant flag directly.

Also remove the need for a post-config by setting up the HltROBDataProviderSvc correctly in the first place.

cc @aporeba @tamartin @wiedenma