Built-in support for Elastic Common Schema

[jhannes]

https://github.com/elastic/ecs-logging-java

https://www.elastic.co/blog/introducing-the-elastic-common-schema

Need custom MDCProvider supporting objects to work.

Should support:

• base fields
• Core log fields
• Some host core fields
• Some http fields from HttpServletRequest MDC
• Some url fields from HttpServletRequest MDC
• Optionally useragent fields from HttpServletRequest MDC
• Some user fields (from Principal MDC?)
• useragent.original from HttpServletRequest MDC (perhaps only in access log?) + optionally other useragent fields