Deliver logs in JSON to CloudWatch

It would be very nice to have the logs published to CloudWatch in JSON format (for example, such as: https://docs.aws.amazon.com/lambda/latest/dg/java-logging.html). Otherwise, it is very hard to sort through them.

This is somewhat related to #226.

If we find a nice way of logging which brings the most (useful) information as possible, other language plugins can adopt it.

先檢視 issue 中連結的 AWS Lambda Java logging 範例以及相關的 issue #226，以釐清所需的結構化欄位與範圍。接著檢查 plugin 現有的 logging 入口點；完成的標準是將 logs 以實用的 JSON 格式傳送到 CloudWatch，並採用其他語言 plugin 也能使用的方法。

由索引模型根據 Issue 內容生成。