Optional parameters are not optional in method signatures

[crenshaw-dev]

WorkflowServiceApi.listWorkflows, for example, requires all parameters even though all but namespace is optional.

This causes several issues:

1. ugly code, with a bunch of parameters specified for every call
2. duplication, with parameters specified in multiple places (unless the user abstracts them out)
3. upgrade difficulty, because otherwise-insignificant method signature changes will break calls
4. uncertain behavior, because without thoroughly investigating argo-server code, it's unclear what values are the correct defaults

I suspect this is either an OpenAPI-Generator bug or config issue. If I generate a scala client with OpenAPI-Generator's scala-akka plugin, the parameters are Options defaulted to None.