[REQ] Allow headers to be visible in swagger even if the ý are implicit

Is your feature request related to a problem? Please describe.

implicitHeaders makes the Spring generator not add the explicit parameters but it also seems to remove them from the generated swagger. I would like implicit headers to be shown as header parameters in the generated spec but not explicit in the method signatures,

Additional context

The concrete use case now is that we have a number of X-.... headers that we would like to be shown explicit in the parameters of the swagger documentation but we are handling them globally in a number of filters and interceptors.

Start by tracing how implicitHeaders is handled in the Spring generator and how its output contributes to the generated Swagger/OpenAPI specification and method signatures. Done means implicit headers appear as header parameters in the generated spec while remaining absent from generated method signatures; add or update coverage for both outputs.