Allow for multiple GPU training

[romeokienzler]

Is your feature request related to a problem? Please describe. Cannot use multiple GPU

Describe the solution you'd like Allow for multiple GPU training

reported by @biancazadrozny

[takaomoriyama]

Testing with multi-GPU multi-node environment (CCC/LSF). Use blaunch.sh and ddp_wrapper.py.

Example: 4 nodes, each node has 8 cores and 2 GPUs

$ jbsub -q x86_6h -cores 4x8+2 -require a100,infiniband -mem 40G blaunch.sh $PWD/ddp_wrapper.py terratorch fit --config sen1floods11_vit.yaml --trainer.num_nodes 4

[romeokienzler]

@takaomoriyama please create PR and add the launch script(s) to the examples folder