Ability to export traces into console (or other exporter)

[jcchavezs]

I wonder if there is (or there should be) a way to display traces in console for our agents. It is quite useful when debugging.

More so I'd like to know if we should be able to send traces to multiples destinations, again for debugging purposes. I know the collector is supposed to do that but sometimes you also want to check what goes into the collector.

Ping @adriancole @davexroth @mohit-a21 @pavolloffay

[pavolloffay]

OTEL collector support logging exporter and fan out to multiple backends. Configuring a similar capability in an agent is also useful, especially for running locally.

If the upstream project on which the agent is based supports multiple exporters then the config should ideally allow it as well.

[jcchavezs]

Since we settle on Config.Reporting.Endpoint I think it is a good opportunity to do this in a uniform way, for example we could say /dev/stdout for console and /path/to/myfile for file exporter. That would be pretty consistent with current implementation which uses zipkin endpoint for http and attempt touse OTLP for GRPC. Notice where is a challenge for /dev/stdout as it is not consistent but as described in https://unix.stackexchange.com/questions/36403/how-portable-are-dev-stdin-dev-stdout-and-dev-stderr

/dev/stdout [...] it is not POSIX, although many actual shells (including AT&T ksh and bash) will simulate it if it's not present in the OS

Ping @davexroth @mohit-a21

[pavolloffay]

partialy done, now the config has exporter type property. We could add logging/console option