[sdk-platform-java] Add showcase testing for logging on stream cases

Basic logging testing are included in https://github.com/googleapis/sdk-platform-java/pull/3403 for unary calls.
Test cases are missing for server side streaming, client side streaming and bidi-streaming.

We need more test coverage for logging behaviors on other type of calls beside unary calls.

Also, consider refactor showcase test to not depend on a TestAppender, but rather capture log outputs from console. This will allow logging implementation classes like GrpcLoggingInterceptor to be not public.