Moving from GitHub Pages to GitLab Pages

The recent resurrection of GitLab CI and Pages across this lab.allmende.io instance allows to reconsider moving the page deployment to GitLab pages. The story will roughly follow the procedure from degrowth/hub.degrowth.net#1, but will have to adapt to the fact of switching platform providers. It will go roughly as follows:

• Mirroring the repository to GitHub is disabled
• The site builds by a GitLab CI/CD example for this Deno project
• The custom domain is migrated here
• Mirroring credentials are removed on GitHub
• GitHub workflows are removed

Reference for the denoland/deno image:

• Won't run in Gitlab CI · Issue #49 · denoland/deno_docker
• how to use deno docker in gitlab runner? · Issue #59 · denoland/deno_docker
• Repurpose DENO_DIR to deno's user home · Issue #109 · denoland/deno_docker