Make braket_container.py thread safe

[sterseba]

Describe the feature you'd like
The braket_container.py script to launch the user-provided algorithm script is not thread safe, currently. When running a multi-node job with parallelization through MPI (the hyperparameter sagemaker_mpi_enabled makes SageMaker to invoke the braket_container.py with mpirun), this can create race conditions in paritcular in the step to download, extract and make available the user-provided code, when running a multi-node job.

The braket_container.py script should be made thread safe to account for jobs running on multiple instances or (GPU) cores with sagemaker_mpi_enabled=True.

How would this feature be used? Please describe.
The user shouldn't have to worry about this feature and, specifically, shouldn't have to change the braket_container.py script if they want to use MPI support for the jobs.

Additional context
There is an example for a simple workaround for this issue in the amazon-braket-examples repository. I have created an issue there to document this doesn't ultimately solve the problem. But, actually, I think this should be addressed here.