Publish documentation to GitHub Pages

[ptheywood]

As an alternative to read the docs, the documentation can be published to GitHub Pages via actions. This will remove the adverts seen on free RTD.

This adds a new GitHub Action workflow, Publish.yml, which on push to the main branch, builds the documentation and if the build is successfull the generated html is commited to the gh-pages branch.

This will then be available via a github pages, initially at https://n8-cir-bede.github.io/documenation (I think).
If this route is to be pursued, the workflow can be ammended to also set the CNAME option, allowing the documentation to be published at a custom (sub)domain, such as bede-documentaion.n8cir.org.uk?.

To demonstrate this worked, my fork's main repository currently contains a (slightly modified) version of the action demonstrating it works, which hosts the content at https://ptheywood.uk/bede-documentation/ https://bede-docs-demo.ptheywood.uk/ (This will not be permanent).

A similar example showing the use of a custom subdomain can be found at https://docs.flamegpu.com/, which sets docs.flamegpu.com as the cname on https://github.com/FLAMEGPU/FLAMEGPU2-doc.

Todo:

• Consider using force_orphan: true with option of peaceiris/actions-gh-pages
• Select the subdomain to use (discussions required)
• Update the PR with the CNAME set + html_baseurl in conf.py
• Get the appropraite DNS settings applied (requires access from others)
  • GitHub Pages Docs:Custom Subdomains, Configuring a subdomain
• gh-pages may need to be enabeld in the repository settings (directed at the gh-pages) branch.

Once merged:

• Update RTD to redirect / link users to the canonincal CNAME url.
• Update website content which currently links to RTD to link to the subdomain cname.

This will close #10 and close #8

[ptheywood]

I've adjusted the demo to host the page at a subdomain: https://bede-docs-demo.ptheywood.uk/ showing how it could work. This will show https warnings until certificates have propagated.

I've reached out on slack to enquire about the domain name other bede support would be keen for, suggesting bede-documentation.n8cir.org.uk, or bede-docs.n8cir.org.uk initially.