Standalone version of 3dcnn_ptl for local training

[oleschwen]

A non-NVFlare version of the 3dcnn_ptl application code for local training would be useful to know that the local training uses essentially the same code as the swarm training.
Implementation could be similar to the minimal_training_pytorch_cnn application code.

AC:

• 3dcnn_ptl application code capable of running a local training in the nvflare-pt-dev:3dcnn docker container