Add Sphinx Documentation to Github Pages for Releases

[tkilias]

Background

• Currently, we only add the Sphinx documentation to Github pages for the main branch. We need the same for released versions.

Acceptance Criteria

• Add Github Action to add Sphinx Documentation to Github Pages for Releases
• Generate overview pages which shows the links to documentation for all available versions
• Because of ongoing trouble with the deploy-to-github-pages.sh shell script, please rewrite it in python3

[tkilias]

We decided to move this functionality to its own repository. So, this repository only requires to install the new tool and run in CI.

[tkilias]

depends on https://github.com/exasol/sphinx-github-pages-generator