Publish documentation on different release versions

**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
- ...

Start by locating the repository's documentation sources and GitHub Pages publishing configuration, then review how releases are published. The work is done when ARC42, User, API, and Admin documentation is available for each release, an index selects former versions, and the latest version is the default.

Written by the indexing model from the issue text.