Docs section for SLURM troubleshooting

[awaelchli]

What does this PR do?

Fixes #14781

My proposal is to add a section to the docs that explains the most likely cause for hangs.
Ideally we would provide a useful error message. The issue with a concrete solution is here #10150 and here #14078. However, these still can't eliminate all user error, especially regarding the setup of the SLURM submission script.

@Felonious-Spellfire for review of the language and structure.

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cc @Borda @rohitgr7 @Felonious-Spellfire @akihironitta