HPCC-25892 Update standard log columns in container mode

- Removes "prefix" field and adds log "class" field to standard log
- Updates helm/examples/logging readme

Signed-off-by: Rodrigo Pastrana <rodrigo.pastrana@lexisnexisrisk.com>

system/jlib/jlog.hpp

@@ -310,7 +310,12 @@ typedef enum
 #define MSGFIELD_STANDARD LogMsgField(MSGFIELD_timeDate | MSGFIELD_msgID | MSGFIELD_process | MSGFIELD_thread | MSGFIELD_code | MSGFIELD_quote | MSGFIELD_prefix | MSGFIELD_audience)
 #define MSGFIELD_LEGACY LogMsgField(MSGFIELD_timeDate | MSGFIELD_milliTime | MSGFIELD_msgID | MSGFIELD_process | MSGFIELD_thread | MSGFIELD_code | MSGFIELD_quote | MSGFIELD_prefix)
 #else
+
+#ifdef _CONTAINERIZED
+#define MSGFIELD_STANDARD LogMsgField(MSGFIELD_timeDate | MSGFIELD_milliTime | MSGFIELD_msgID | MSGFIELD_process | MSGFIELD_thread | MSGFIELD_code | MSGFIELD_quote | MSGFIELD_class | MSGFIELD_audience)
+#else
 #define MSGFIELD_STANDARD LogMsgField(MSGFIELD_timeDate | MSGFIELD_milliTime | MSGFIELD_msgID | MSGFIELD_process | MSGFIELD_thread | MSGFIELD_code | MSGFIELD_quote | MSGFIELD_prefix | MSGFIELD_audience)
+#endif
 #define MSGFIELD_LEGACY LogMsgField(MSGFIELD_timeDate | MSGFIELD_milliTime | MSGFIELD_msgID | MSGFIELD_process | MSGFIELD_thread | MSGFIELD_code | MSGFIELD_quote | MSGFIELD_prefix)
 #endif