Mount IsaacLab submodule directory (#106)

## Summary
Fixes the CloudXr instances not being found when entering AR mode.

The submodule we have access to in the submodule was just a copy. For
some workflows we need access to on-the-fly changes on the host side.
One example is the CloudXr server we launch on the host in the submodule
directory which only then creates runfiles which in turn are required by
IsaacLab within the container.

Changes breaking this made it in through
[MR](https://github.com/isaac-sim/isaac_arena/pull/71/files#diff-f6c013bcc6aafeba1cb42835e7185514a3a794d17cae289b990abd74955796ecR97-R101)

Author: cvolkcvolk

docker/run_docker.sh

@@ -129,6 +129,7 @@ else
                     "--gpus=all"
                     "-v" "./docs:${WORKDIR}/docs"
                     "-v" "./isaac_arena:${WORKDIR}/isaac_arena"
+                    "-v" "./submodules/IsaacLab:${WORKDIR}/submodules/IsaacLab"
                     "-v" "$DATASETS_HOST_MOUNT_DIRECTORY:/datasets"
                     "-v" "$MODELS_HOST_MOUNT_DIRECTORY:/models"
                     "-v" "$EVAL_HOST_MOUNT_DIRECTORY:/eval"