Improve performance of analytics workflow

[wouterjdb]

This PR addresses the slow loading of many realization in the analytics workflow.

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Contributor checklist

• [x] :tada: This PR closes #261.
• [x] :scroll: I have broken down my PR into the following tasks:
  • [x] Add ThreadPool to load realization with multiple threads
  • [x] Refactor save_iteration_analytics()
  • [x] Refactor make_dataframe_simulation_data()
  • [x] Remove plotting
  • [x] Test speed (1/2 min for ~200 realizations, three vectors times two metrics)
  • [x] Full Norne model currently gives an error. This needs to be solved first.
• [ ] :robot: I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR.
• [x] :book: I have considered adding a new entry in CHANGELOG.md.
• [x] :books: I have considered updating the documentation.

Open issue related to stability: #267

[wouterjdb]

Initial testing didn't show promising results. I tried doing some initial profile using cProfile, but for some unknown (to me) reason I'm not getting any results. To be continued...