[Swift] Add debugPrint mode

[d-date]

Description

With using Alamofire, we can print cURL command from request object in console.
It's useful to debug network not only for iOS developers but also for server-side engineers.

However, if we include print(request) without any condition, user cannot avoid including cURL printing into release build.

To avoid this, we should add static var debugPrint: Bool option to SwaggerClientAPI class so that user can choose whether print request or not.

In use case, when building app with debug build, all request can be printed in your console, and not printed in release build setting with preprocesser macros.

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