Adresses #873

Changes proposed in this pull request:

• Update eland-requirements.rst (reference)
• Update MVS_kpi_categories.csv: Add category "files"
• Update MVS_kpis_list.csv: All output files
• Add the output file sections in the RTD simulation_outputs.rst
• Adapt conf.py to include the output files in RTD properly

The following steps were realized, as well (if applies):

• Use in-line comments to explain your code
• Write docstrings to your code (example docstring)
• ❌ For new functionalities: Explain in readthedocs
• ❌ Write test(s) for your new patch of code (pytests, assertion debug messages)
• Update the CHANGELOG.md
• Apply black (black . --exclude docs/)
• ❌ Check if benchmark tests pass locally (EXECUTE_TESTS_ON=master pytest) -> only RTD changes

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• Done

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