Docs: Add MPIEvaluator tutorial for multi-node HPC systems, including DelftBlue

[EwoutH]

This PR introduces a two-part tutorial for the MPIEvaluator introduced in #299.

The first part (d26f54e) focuses on the general setup and usage of MPIEvaluator in multi-node HPC systems:

• Utilizing the new MPIEvaluator for HPC systems.
• Instructions on setting up the necessary environment, including the installation of OpenMPI and mpi4py.
• Detailed step-by-step guidance for defining, testing, and executing a model on an MPI cluster.
• Demonstrations of saving and loading results using pickle.

The second part (9e04566) extends the tutorial with specific instructions for the DelftBlue supercomputer, which uses the SLURM scheduler:

• Detailed guide to crafting a SLURM script specifically for the DelftBlue supercomputer.
• Insights into DelftBlue's capabilities and hardware specifications.
• Comprehensive steps for environment setup, user authentication, file transfers, job scheduling, and retrieval of results on DelftBlue.

Together, the tutorial provides an end-to-end guide for leveraging the MPIEvaluator on HPC systems.

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[EwoutH]

I have no idea why the ReadtheDocs build is failing.

nbsphinx.NotebookError: NoSuchKernel in indepth_tutorial/mpi-evaluator.ipynb:
No such kernel named python3

I compared the notebook metadata to general-introduction.ipynb and directed-search.ipynb, and it looks practically identical. directed-search.ipynb:

 "metadata": {
  "kernelspec": {
   "display_name": "Python 3 (ipykernel)",
   "language": "python",
   "name": "python3"
  },

mpi-evaluator.ipynb

 "metadata": {
  "kernelspec": {
   "name": "python3",
   "language": "python",
   "display_name": "Python 3 (ipykernel)"
  },

[EwoutH]

One of those cases you spend more than an hour to find that one exact line code is a sea of possible configuration options. But it now works.

Ready for review, merge (by fast-forward) after #299.

[coveralls]

coverage: 80.585%. remained the same
when pulling 0616fca on MPI-tutorial
into 65e0fc0 on master.

[EwoutH]

@quaquel Thanks for reviewing, I implemented the feedback and cleaned up the commits. If you approve we can fast-forward merge.

Edit: CI doesn't run on docs changes, and currently there is a required check which will prevent merging. Personally I don't think we need the required checks, we won't merge (blindly) when CI fails anyway.

[EwoutH]

Required statuses must pass before merging

Can you remove the required check? Otherwise I cannot merge.