Publish documentation for each stable branch + current development (master)
Currently we only publish docs to master, and gitlab still lacks proper support to deploy to a separate URL depending on which branch the CI is running from.
See upstream gitlab bug report.
Said upstream bug report suggests a workaround which might be plausible, which involves using the cache. The problem with this is if ever the cache gets deleted (which is supposed to be expected), we would have to manually trigger CI for every stable branch in history to regain the docs.