Migrate documentation to `mkdocs-material`

[JR-1991]

[!IMPORTANT]
This PR is still a draft and work in progress

Overview

This PR introduces the mkdocs-material to pyDataverse, which serves as a modern substitution for ReadTheDocs. It looks better and provides more functionality to the docs itself. Plus, mkdocs can be easily integrated into GitHub Pages, removing the third-party dependency of ReadTheDocs (although surely possible, if wanted). This PR also implements an automatic generation of the API reference based on the given docstrings.

TLDR

• Migrate docs to mkdocs-material
• Add API reference generation based on docstrings

How can I take a look at the new docs?

To check the current state of the docs, please run the following commands:

python -m pip install mkdocs-material
mkdocs serve

You should be presented with a localhost link to paste into your browser.