logging: Add subsystem to log API (#19002)

Create new code paths for multiple subsystems in the code. This will
make maintaing this easier later.

Also introduce bugLogIf() for errors that should not happen in the first
place.

cmd/api-errors.go

@@ -2519,7 +2519,7 @@ func toAPIError(ctx context.Context, err error) APIError {
 		// Make sure to log the errors which we cannot translate
 		// to a meaningful S3 API errors. This is added to aid in
 		// debugging unexpected/unhandled errors.
-		logger.LogIf(ctx, err)
+		internalLogIf(ctx, err)
 	}
 
 	return apiErr