question: Custom gather method
context: How do I correctly override gather behaviour?
  Ideally, I would have a single place where I should specify new method and it would work with dp, ddp and ddp_spawn.
answer: Managed to get this working for dp by subclassing DataParallelPlugin and passing it to trainer. Although this approach requires individual plugins for each accelerator, it would be nice to have a way to set this for all accelerators at the same time.