Implementation of non-currently-supported decays in gg4l process via change of pdg ID in LHE files AGENE-2156

This MR is to support 4e, 4mu, 4tau and 2l2tau decays in the gg4l process available in Powheg. The support of such decays is made via a post-processing of the LHE files as already done for the EW V+jet setup, see !45492 (merged).

The installation of the gg4l process is instead being followed up in

This setup (4e and 4mu decays only) is quite urgent for the run 3 HZZ analysis.

Tagging @carcange @sabidi @goblirsc for the HZZ side.

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