Adding HH4b chains with b-jet preselection capabilities in the jet slice

This MR includes all the changes to the jet, MET and unconventional tracking signatures to run b-jet trigger preselections before the jet FS tracking. An empty step has been added in the MET and unconventional tracking reco steps in order to align the reconstruction with the new roiftf step. For testing purposes, a first set of asymmetric HH4b chains with b-jet preselections has been added to the Run 3 dev menu.

Additional changes to ChainMerging.py were also made. These changes allow to handle these new empty steps cases and they also solve some bugs that miraculously never appeared in the past. :)