polkit Documentation as Gitlab Pages added in CI jobs

Job that creates and deploys polkit API documentation/manpages as html to Gitlab Pages. The job is triggered by creating a tag.

The tag-trigger is not ideal as there may be other tags than those defining a Release, however it is sufficient now.
[further work] It might be possible to divide the job into "release" and "deploy" stages. The "deploy" stage might be triggered only if "release" stage is successful (and of course, the "release" stage only happens if making a new release).