[docs] Implement initial mkdocs config, gh-pages workflow and initial content

[jh-RLI]

Description of the issue

We decided to migrate the documentation in smaller steps. In the branch #1303 i started to implement a complete migration but this will take more time to be complete.

This PR is now only implementing:

• basic configuration of mkdocs
• the gh-pages workflow, which updates the documentation every time it is published (possibly also with versions like production, development - at the moment it is updated when the code is merged into development)
• Add structure and content to show information about API and supported data types

Workflow checklist

• I am aware of the workflow in CONTRIBUTING.md