Publish documentation on different release versions

[ds-jleyh]

As a Contributor and Developer
I want to access the documentation in different version on github pages
so that always see the corresponding documentation to a certain version

Hints / Details

Acceptance Criteria

• Documentation (ARC42/User/API/Admin) is published for each release
• Each release is accessible for users. (index page to select former versions)
• Latest version is shown as default.

Out of Scope

• ...