client side code generation from openapi/swagger specification

[Relivian]

Currently only server side code generation is supported.
This issue is to discuss topics and todo's (e.g. supported languages, build environment etc)

[stevehu]

It has been discussed for a long time within the team but we never got a chance to add this to the light-codegen. The idea is to add the client stub generator and then add it to the light-portal or any customized marketplace from our customers so that API users can look at the spec of interested API and generate the stub and download it locally to start the consumer application.