TheP8I: Lund fragmentation in Herwig

Dear all,

This merge request provides a piece of JobOptions and an example needed to run TheP8I with Herwig in the Athena.

TheP8I is an interface between ThePEG2 and Pythia8 that allows to use the Lund fragmentation model inside ThePEG2 and Herwig7.

The codes for the TheP8I can be found here:

https://gitlab.cern.ch/TheP8I/TheP8I

The physics behind is partially studied in https://arxiv.org/pdf/1908.10811.pdf

In addition to this MR the TheP8I was tested using

https://gitlab.cern.ch/averbyts/mcjoboptions/blob/master/830xxx/830006/mc.H7_H71-DEFAULT_Zjets.py

Best regards,

Andrii

Taging @fsiegert @ewelina @amoroso @jchapman