Merge requests related to Powheg

Output changes approved by offline SW coordinators

MR submitted by non ATLAS account

MR is included in mainGAUDI-OMR nightly build

MR is included in mainGAUDI nightly build

MR is included in ACTS nightly build

This MR contains new configuration and so should be reviewed by relevant experts.

Merge Requests that only remove legacy configuration, and so should not impact any currently supported workflows