Implementing Json log exporter

[ohadza]

I created a clean PR, for the changes that were made after this PR #3685
(And will close the non-relevant)
for the Issue: Logging POC for log4j, logback, pita

[jkwatson]

This will end up putting a whole lot of log lines on a single log output. I don't think that's what I'd expect to happen. I think this should only output one log per line, rather than cramming the whole json body into one line.

[jack-berg]

I remember reading a PR from a while back that part of the intent of these loggers is that another process could parse each log line as a Resource{type} message. If that is indeed part of the intended use case of the log exporters, we shouldn't break convention.

[jack-berg]

The idea in general of logging exported LogRecords is cyclical when thinking about it from the perspective of application logs: an application logs a message -> an appender feeds to the otel log sink -> the log exporter logs the message in json format -> an appender feeds to the otel log sink

I think its only really practical to use one of these log exporters if you're collecting events as LogRecords rather than application logs.

[jkwatson]

Hmm. I see the point. We should have the equivalent of the LoggingSpanExporter that will just mirror the logs back to JUL, one per line, which can be very useful for debugging. But, of course, problematic if used with a JUL appender! Perhaps that one (which I know is not this one) should just use stdout.