Create Middleware to provide SwaggerUI OpenAPI endpoint

[987Nabil]

A middleware should be added, that creates an endpoint that returns an html document that renders a given OpenAPI instance.
We should not add any library dependencies for that, but rather use unpkg.
We can give a default value for the swagger ui version, but should make it configurable.
API for the middleware should look somewhat like this

def swaggerUI(api: OpenAPI, path: String, version: String = "4.5.0")

This is blocked by #2470