Set up a documentation page

[saig0]

Description

Currently, the project doesn't have proper documentation. There is only the README with some basic information. Since the project will be used by two other Camunda projects, we should provide documentation that covers relevant parts, like bootstrapping or internals about the usage.

First, we need to set up a documentation page. We should use Docusaurus like the FEEL-Scala project and Camunda Cloud.