docs(core): publish mkdocs with github pages

[paddy74]

This PR configures MkDocs as the project's documentation site, including referencing existing .md files and docstrings.

• Initialize MkDocs
• Create MkDocs plugin mkdocs-external-files
• Extend mkdocs.yaml with hooks.py
• Add additional properties to _version.py
• Automate publication to GitHub Pages using .github/workflows/docs.yaml
• Add badges to the README.md