TriggerJobOpts: cleanup TriggerConfigGetter and flags

This is rather big cleanup of TriggerConfigGetter:

• Replace TriggerFlags.dataTakingConditions by ConfigFlags.Trigger.availableRecoMetadata: this flag is used to indicate the trigger systems that are enabled during reconstruction. It is set based on the L1/HLT keys in COOL or the metadata in the input file.
• Remove obsolete metadataItems setting as discussed with @tamartin (the key names are not relevant anymore, and we are setting this elsewhere already).
• Deprecate TriggerFlags.configForStartup: this flag was used to indicate whether trigger keys can be found in COOL. But this is essentially the same check as availableRecoMetadata performs already. The flag itself is still there but will print a WARNING if set. Once this is merged, should update reprocessing shifter instructions to not add this to the AMI tag anymore (discussed with @mark).
• Fix the broken getKeysFromCool method in TrigConfigSvc.

I did not re-implement the setting of the DQMonFlags based on the available systems. If this is really needed still for the legacy monitoring it should be done in the relevant DQ job options. There are also a few TODO items left in the code that will be cleaned up separately. And once the dust has settled, we can think about migrating this to CA.

Relates to ATR-23102.

cc @rbielski