[Feature](group commit) Support table property "group commit data bytes" (#29484)

fe/fe-common/src/main/java/org/apache/doris/common/Config.java

@@ -515,6 +515,10 @@ public class Config extends ConfigBase {
             "Default commit interval in ms for group commit"})
     public static int group_commit_interval_ms_default_value = 10000;
 
+    @ConfField(mutable = false, masterOnly = true, description = {"攒批的默认提交数据量，单位是字节，默认128M",
+            "Default commit data bytes for group commit"})
+    public static int group_commit_data_bytes_default_value = 134217728;
+
     @ConfField(mutable = true, masterOnly = true, description = {"Stream load 的默认超时时间，单位是秒。",
             "Default timeout for stream load job, in seconds."})
     public static int stream_load_default_timeout_second = 86400 * 3; // 3days