Add AOD output option

This adds the option to spit out a slimmed down AOD, which might be useful to test other simpler algorithms before porting them into the main easyjet sequence. For now it just dumps the EventInfo and the same jet collection we usually write to an ntuple.

I had to do a bit of magic along the way:

• When this is enabled I use PoolReadCfg rather than xAODReadCfg. It seemed like the later might be working, actually, but it also printed a warning saying I should not use it 🤷
• I had to make a deep copy of the view container that we usually write out. Maybe there's a smarter way to do this, but it failed to write anything otherwise. The class for the deep copying could easily be turned into a template if we need this for more objects. Since I had to make a new jet collection, I called it EasyJets 😀

I also fixed a quasi-bug where the argument parser wouldn't print all its arguments when you asked for --help. I think the issue was that we'd call validate_args without providing a configuration file, which would throw an exception and thus only process the help for the first option that overwrites a config file option.