Chore: configure branch protection rules for `gh-pages`

[peteski22]

The gh-pages branch is used by GitHub to host the mcpd github.io docs site.

• Configure branch protection rules so that it isn't accidentally removed etc.
• Ensure it's captured in developer related docs

[peteski22]

Discussing this with @macaab26 and it seems we should instead try to update the GitHub Action to use artifacts instead via:

• actions/configure-pages
• actions/upload-pages-artifact
• actions/deploy-pages