Change CI such that Docs are no longer published to gh-pages

Currently, documentation for the source repo (`main` branch) is in the docs/ directory. The CI builds static docs based on the docs/ directory using sphinx. These docs get built into the build/html directory and packaged into a docs.zip. The docs.zip is not used for publishing but is instead stored as an artifact (for a job or release). It contains exactly one version of the docs. The docs in the build/html directory get moved to their respective folder in .github/pages which gets published to `gh-pages`. The GitHub pages site is built from the `gh-pages` branch and the switcher.json allows for switching between different versions (e.g. v1.0, v1.1). This is an issue, for example with the blueapi repo, as it leads to a large repo size which takes a long time to clone.

To address this issue, but still have access to documentation of previous versions, the suggested change is to create the entire site by consuming multiple docs.zip files (incl the one that has just been generated).