Increase docker shared memory

[mkhansenbot]

This fixes an error when running with multiple GPUs from a docker container. This increases the shared memory given to the docker container to 1 GB by default.

Tested with the following:

# run container
cd OmniIsaacGymEnvs
docker/run_docker_viewer.sh

# inside container, run single GPU (Headless)
/isaac-sim/python.sh scripts/rlgames_train.py task=Ant headless=True

# inside container, run with multi_gpu=True
/isaac-sim/python.sh -m torch.distributed.run --nnodes=1 --nproc_per_node=4 scripts/rlgames_train.py headless=True task=Ant multi_gpu=True

[mkhansenbot]

@kellyguo11 - any update, can this be merged?