ATLASRECTS-6241 : Split egamma config into 3 parts. The actual Reco, the output Item Lists, the Thinning

Split egamma config into 3 parts. The actual Reco, the output Item Lists, the Thinning.

For now add a steering to combine these 3 and use that

@emoyse since you wanted to look at code the 3 files are

1. egammaReconstructionConfig.py
2. egammaOutputConfig.py
3. egammaxAODThinningConfig.py , in a next iteration we will add the cell thinning here.

For now the egammaSteering is including all these 3 and then this is what the RecoSteering sees as per todays instructions.

Ignore the LRT ones as these are in R&D state for now as far as the new Config is concerned. if we have it will also for now go into the steering.

ping @turra , @jdevivi