log_event: added required fields to expose group metadata to client code

Signed-off-by: Leonardo Alminana <leonardo.alminana@chronosphere.io>

Author: leonardo-albertovich

include/fluent-bit/flb_log_event.h

@@ -38,6 +38,8 @@
 #define FLB_LOG_EVENT_GROUP_END           (int32_t) -2
 
 struct flb_log_event {
+    msgpack_object  *group_attributes;
+    msgpack_object  *group_metadata;
     msgpack_object  *raw_timestamp;
     struct flb_time  timestamp;
     msgpack_object  *metadata;