test: add showcase testing for logging on stream cases

[zhumin8]

Basic logging testing are included in #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.