Added a MultiCPU SLURM example using Accelerate Launch and MPIRun

[okhleif-IL]

What does this PR do?

This PR adds a multicpu SLURM example in the examples/slurm folder using Accelerate and MPIRun. This script can run a multicpu SLURM training example on the complete_nlp_example.py script.

This PR also fixes a minor typo in all other SLURM example .sh scripts regarding activating the environment.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
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[muellerzr]

Thanks! Overall LG2M, bar one nit

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[muellerzr]

Thanks!