Enhancement for Compact JSON

The current implementation seems to yield a pretty printed output of the ECS JSON. Would it be possible to optionally configure the layout to output compact JSON?

Perhaps it would be valuable to add analogous features with the same capability and intent as those related to the "compact", "eventEol" and "endOfLine" etc settings which are available on the OEM JSONLayout.

See https://logging.apache.org/log4j/2.x/manual/layouts.html where pretty print vs compact format is discussed.

首先找到 ECS JSON layout 的实现，并将其配置与 issue 中引用的 OEM JSONLayout 设置进行比较。先阅读链接的 Log4j layout 文档；完成的标准是能够将 ECS JSON 输出配置为紧凑 JSON，其行为与相关的 compact、eventEol 和 endOfLine 选项保持一致。

由索引模型根据 Issue 内容生成。