Improve jet config integration with newreco steering

As discussed in ATLASRECTS-6248 we make so by default the jet config does not invoke configuration for its upstream dependencies. A flag is introduce in the new module JetConfigFlags.py to re-enable this behavior (can be useful for jet developers).

Also removing the saving of jet collections to xAOD in JetRecoSteering.py : it was decided that jets are not saved anymore, but build during derivations. Instead a utility function is provided in case one still wants to save jets during test jobs.

Other very minor technical updates.