Add option to use powhegLHEReader for Herwig7 in Herwig72ConfigLHEF.py

Added an option to Herwig7Config.lhef_powhegbox_commands(..) to use a special LHEReader to Herwig7, which is able to propagate multiple event weights. The actual reader has to be delivered via a gridpack.

This is urgently needed for a new Powheg+Herwig7 W sample

Tagging @ewelina

added 21.6 Generators labels

This merge request affects 1 package:

• Generators/Herwig7_i

added review-pending-level-1 label

CI Result SUCCESS (hash bb9d5180)

	AthGeneration
externals
cmake
make
required tests
optional tests

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AthGeneration: number of compilation errors 0, warnings 1
For experts only: Jenkins output [CI-MERGE-REQUEST 44750]

merged

mentioned in commit 058a7ab2

Thanks Dominic. The next build is planned for Monday.

added sweep:ignore label