Added Ds3PiPhi modes
This is to add the channel Ds3PiPhi to the ntuples of the \eta and \eta^\prime analysis under the Charm WG.
The production already exists under the name etadecays
(https://lhcb-analysis-productions.web.cern.ch/productions/?wg=charm&analysis=etadecays), and this wouldn't supersede previous MRs, it would live alongside the already-created ntuples.
The analysis is currently in RC and we are targeting an unblinding by late January/early February at the latest, so I'd appreciate it if we could prioritize this.