OpenAPI integration for Documentation

[DGuhr]

Oliver just asked me to open this ticket while presenting spring modulith at JUG Münster, so here it is:

It may be of value if the already great documentation support could also integrate possible OpenAPI definitions, for each module and/or for all modules, so not only the controllers, but kindof an integration of the OpenAPI frontend ("swagger-like").

Happy to discuss this proposal in more detail in the future, for now I'll listen again.