Muzzle mismatch logs should be warnings in tests

[mateuszrzeszutek]

Resolves #534

This change actually changes muzzle mismatch logs to warnings everywhere, not only in tests - but hides them behind the otel.javaagent.debug config.

[iNikem]

If that actually works as intended, then 👍

[trask]

I don't totally love altering the log level based on the debug flag. If I see something logged at warn when the debug flag is on, I think I'd be confused not to see that also logged when the debug flag is off, and info+ is (generally) being logged.

But I don't hate it either 😄, so good with it until (if) we think of something better.

[trask]

👍

[iNikem]

But it is our original desire: to have muzzle logs on WARN, but do not log them by default. Which means that some WARN logs will be absent anyway when enabling only info or debug as default logging level.

[mateuszrzeszutek]

I don't totally love altering the log level based on the debug flag. If I see something logged at warn when the debug flag is on, I think I'd be confused not to see that also logged when the debug flag is off, and info+ is (generally) being logged.

Hmm, maybe it's just a matter of naming the debug flag more clearly: if we used something like otel.javaagent.log-everything instead of otel.javaagent.debug the intent would be more obvious (don't treat the log-everything name seriously, that's just an idea 😅 )

[trask]

I think ideally we would do something like #566 (comment)

log at a higher level than DEBUG if all instrumentation for a particular library (e.g. both cassandra-3.0 and cassandra-4.0) are muzzled

also, our debug logging is very verbose, which makes things get lost easily, even info/warnings

we could consider not using the debug flag during tests (by default), especially after #1643, when we can have separate log level for testing code (e.g. nice to log full spans that are received from exporter)

just stuff to think about / come back to later

i'm good with this PR as-is, it does address a real need 👍