Expose logger_instance_uuid

To allow tying it to other things about the log files.

Change-Id: I3e534a5d355ac9232af8cb353730e36952f04cec
diff --git a/aos/events/logging/logger.h b/aos/events/logging/logger.h
index dd10f38..230f773 100644
--- a/aos/events/logging/logger.h
+++ b/aos/events/logging/logger.h
@@ -67,6 +67,7 @@
   }
 
   std::string_view log_start_uuid() const { return log_start_uuid_; }
+  UUID logger_instance_uuid() const { return logger_instance_uuid_; }
 
   // Rotates the log file(s), triggering new part files to be written for each
   // log file.