Migrate from ReadTheDocs to Gitlab Pages

Ethical Ads are now appearing on the Guidebook - placeholders, at least (see screenshots below).

These arise due to hosting the mkdocs-generated site on ReadTheDocs (RTD), see here:

  https://docs.readthedocs.io/en/stable/advertising/ethical-advertising.html

There's info on how to opt out at the bottom of that page here.

Paid Gold Membership for RTD is required to opt out, which is $5 per user.

This issue can be remedied for free by the following steps:

• Migrate from ReadTheDocs to Gitlab Pages (the Gitlab CI config is simple, see here).
• Update DNS to point to the pages-generated site.

This was discussed in an MS Teams > Team Leads chat here.