Ability to use a specific version of openapi generator cli

[sweetb]

I'm not sure when / why / how but the openapi generator CLI recently broke form params where it doesn't set the param before calling the service endpoint, it just passes empty to the endpoint (even though the method takes the appropriate list of params).

I wanted to be able to switch to a specific version of openapi generator, but it is not supported as far as I can tell. I generated the package locally but would love to be able to generate it properly from the github action.