Finalize monorepo setup

[chalin]

This repository is effectively a monorepo: the Docsy theme is maintained from the repo root, while the website lives under docsy.dev. I've already started more cleanly separating concerns earlier by a rework of the packages.json files. I think that one of the last things to do would be to move the Netlify config to be under the website (sub)repo.

And there's more to come. Details TBC.

Tasks

• Relocate and adjust Netlify config
  • [CI] Move Netlify config to docsy.dev subrepo #2437
  • [CI] Drop temp site-copy code and more #2439
• Create release branch
• Adjust Netlify https://app.netlify.com/projects/docsydocs/configuration/deploys#build-settings: set base to docsy.dev, the rest is left to their default values
• Ensure that production deploys from release work
• Ensure that PR deploy previews still work
• Setup main deploy previews
• Validate that main deploy previews get triggered. Done, see: https://app.netlify.com/projects/docsydocs/deploys/69696aa5c113a00008397f91
• Update release-process instructions, add link to main preview, etc. - Update README, contrib docs for deployment and release process #2440
• Update branch protection rules for release, to prevent rebasing - @emckean, could you do this?

Followup:

• Add version to docs index page, bump version to 0.14.0-dev #2441
• Add docs version as a badge #2442
• Add site build info and project build documentation #2444
• chore: Rename 'site' docs section to 'project' and update links, and add task plan #2445