Allow structure logging JSON to be customized

[philwebb]

From https://x.com/jkuipers/status/1840849120874950716

[philwebb]

Several interesting ideas we could consider:

• Should you be able to rename Logstash field names? I assumed they were standard, but it seems the Logstash appender allows renames.
• Should we offer a quick way to include additional fields with static values? Service name is interesting because we do have a way to set that with ECS.
• Should we offer a general MDC filtering mechanism?
• Should we offer a general stacktrace post-processing mechanism?

[mp911de]

You can draw some ideas from https://logging.paluch.biz/ that included stack trace filtering, dynamic MDC inclusion/exclusion and field name handling back from when that project has been active.

[philwebb]

We discussed this today and we'd like to offer some enhancements if we can. I'm not sure how much we'll be able to get into 3.4 at this point. We might take stacktrace post-processing off the table for now.