Provide a Log4j appender for resource logging

LoggerProxy provides logging capability. However, some libraries especially [AWS SDK uses Log4j](https://docs.aws.amazon.com/sdk-for-java/v1/developer-guide/java-dg-logging.html) for their logging.

To enable log4j for resource handler, a Log4j appender should be provided so it can be hooked with Log4j and upload logs to resource provider's CW logs.

先定位 LoggerProxy，並檢視 resource handler 目前如何將日誌上傳至 resource provider 的 CloudWatch logs。接著研究 AWS SDK 的 Log4j 整合，並定義 Log4j appender 必須提供的內容；當以 Log4j 為基礎的函式庫能透過該路徑路由其 resource handler 日誌時，即表示完成。

由索引模型根據 Issue 內容生成。