go/adbc: unify logging config with OTel config

[lidavidm]

What feature or improvement would you like to see?

#2729 adds tracing with its own configuration of log export. We should ideally sink slog logs into OTel as well when possible.

[lidavidm]

Currently to enable logs we look for env vars like ADBC_DRIVER_SNOWFLAKE_LOG_LEVEL. This prints to console. This only works in SO/DLL builds because the logic is in the wrapper that produces shared libraries, and not in the driver/driver framework.

I'm thinking that when OTEL_LOGS_EXPORTER is additionally set (and isn't empty or "none"), then we should use otelslog to direct the logs to OTEL instead. Then they should naturally end up in the OTEL exporter, and ideally in the custom log file. Otherwise we don't add any extra or custom config.

This does have the disadvantage that setting the option inside code won't do anything. We could add a separate path that looks for OTEL_LOGS_EXPORTER and if so, overrides any configured exporter with the otelslog exporter instead. (Code using Go APIs directly can additionally use DatabaseLogging.SetLogger for full control; this would only be for code using the driver over FFI.)

@zeroshade @birschick-bq any comments?