Add documentation for running MESSAGEix on UniCC

[measrainsey]

WIP: migrate my internal guide and documentation on how to run MESSAGEix on the cluster (UniCC) and make some modifications

How to review

For @khaeru and/or @glatterf42 : Read the diff and note that the CI checks all pass.

PR checklist

• Continuous integration checks all ✅
• Add or expand tests; coverage checks both ✅
• Add, expand, or update documentation.
• Update doc/whatsnew.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.0%. Comparing base (7f94f8a) to head (b920f59).
Report is 12 commits behind head on main.

Additional details and impacted files

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- Coverage   77.9%   77.0%   -0.9%     
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  Files        213     213             
  Lines      16512   16512             
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- Hits       12872   12724    -148     
- Misses      3640    3788    +148     

see 7 files with indirect coverage changes

[glatterf42]

Thanks for this extensive guide! Skimming over it, I thought of just a few notes :)

[glatterf42]

It's great to have a section like this, but if the cluster becomes more heavily used, there are more considerations for setting these parameters: in general, slurm will try to optimize its load so that it's running almost always at full capacity. This makes it harder to request lots of resources for extended amounts of time because the system will not be able to squeeze in such a task with other tasks, thus it will likely take longer for the task to be picked up.
I don't know if UniCC is already experiencing the kind of load to make these considerations necessary, but if/once it does, we would likely want to optimize these parameters further to request the minimum necessary that still reduces the run time :)

[khaeru]

Thanks @measrainsey for this valuable contribution!

Some items for follow up:

• One thing I believe we discussed orally was to organize this and the other HOWTO guide in their own docs section.
• I would also like to make sure that the guide teaches users where to find information in the UnICC docs and by using e.g. the man pages for sbatch and similar commands.

But LGTM and make those improvements while addressing #284 et al.