[REQ] [scala-akka-client] Use sttp client to make scala client more generic

Created by: chameleon82

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

Scala has a lot of different clients like akka-http-client, http4s, async-http-client and many others. Code generator can generate client with only few of them and use different templates for it Second problem for scala clients is Json parser which is also hardcoded in every template.

Describe the solution you'd like

It is possible to generate client with wrapper library sttp and client can use any compatible implementation which currently support akka-http, async-http-client, http4s, OkHttp and java clients.

Describe alternatives you've considered

As alternative we can reuse templates as much as possible. For example, models in all scala implementations absolutely the same. Template structure can be redefined like /resources/base_language/language. Unfortunately, mustache template engine works not well with such complex paths.

Additional context

In akka-http-client we already have ApiRequest concept which has it's own definition in sttp library.

@clasnake @jimschubert @shijinkui @ramzimaalej