refactor SimpleLoggerAdvisor

[dev-jonghoonpark]

Modifications:

1. added constructor

Although the LoggerAdvisor documentation mentions the following constructor, the SimpleLoggerAdvisor class did not have it in the code.
I added the following constructor to SimpleLoggerAdvisor:

SimpleLoggerAdvisor(
    Function<AdvisedRequest, String> requestToString,
    Function<ChatResponse, String> responseToString
)

2. changed to use Method References for DEFAULT_REQUEST_TO_STRING and DEFAULT_RESPONSE_TO_STRING

3. changed order variable to final