Add `emit` api for `Logger`

[kmos]

Scope

Introduce emit API for Logger

References

Logs API: https://opentelemetry.io/docs/specs/otel/logs/api/

[inge4pres]

When the emit implementation goes forward, using std.log from the Zig std library might be a good choice.

The docs has an example where a custom logger scope can be attached to the logger and provide a way to send logs to a std.io.writer.

We could adopt a similar way, for example to send LogRecords from the protobuf messages into OTLP bytes stream (when the exporter is configured for it).
If the exporter is configured for a file, the writer would be a file, and so on...