Adding GN2X to FTAG Tools

This merge request aims to add support for running GN2X (and other jet-decoration-based central taggers), via JSON configuration files.

The benefits of this method of tagger configuration are manyfold: namely, enabling analyses to use (as-of-yet un)calibrated taggers, which are available in DAOD and enabling flexible configuration of working points and labels.

More details will be covered here: