[Feature]: Add setup for auto-generating API documentation with sphinx

[tomvothecoder]

Is your feature request related to a problem?

• Add and setup sphinx.etx.autodoc, sphinx.ext.apidoc, sphinx.ext.viewcode, sphinx.ext.napoleon
  • Example config: https://github.com/xCDAT/xcdat/blob/b46c331652ece58c13d00bb524a63f3aae750382/docs/conf.py#L35-L77
• Set docstring format to NumPy style
• Provide examples in documentation

Describe the solution you'd like

No response

Describe alternatives you've considered

No response

Additional context

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