Allow optional prefix in generated spec

[VersBinarii]

This PR addresses this issue.

@sunli829 please review and let me know if this is ok with you

[VersBinarii]

The tests are failing because some rate limits while installing protoc

[VersBinarii]

@sunli829 if you're happy with the approach i could add the options to the swagger_ui and rapidoc functions as well.

[sunli829]

Maybe it's better to do this so that we don't need to change spec, swagger_ui, rapidoc, etc. methods?

 let api_service = OpenApiService::new(TodosApi, "Todos", "1.0.0")
                              .server("http://localhost:3000")
                              .url_prefix("/foo/bar"); // specified url prefix

[VersBinarii]

Very well, that seems cleaner. Let me have a look at it then

[VersBinarii]

Hello @sunli829 , i've updated it as per your suggestion.

[sunli829]

Thanks! 🙂