fixing names of weights in NNLOPS reweighting for HJ Powheg

Dear all,

This is a fix for the NNLOPS reweighting in Powheg HJ

- The nnlops weight-ids need to start with "nnlops-"
  • Only standard naming in Athena is supported for non-nnlops weights : MUR1_MUF1_PDF93330 and similar
  •     Exotic weights are not supported

I tested it for PDF and ME scale variations and it worked fine for me. The weights in the LHE files and the ROOT files in EVNT production looks consistent.

The Athena version for the test was 24.0.12 (main latest)

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