[fix](multi-catalog) add config to disable external DDL (#31528)

from #31453

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

@@ -2216,6 +2216,12 @@ public class Config extends ConfigBase {
         "Sample size for hive row count estimation."})
     public static int hive_stats_partition_sample_size = 3000;
 
+    @ConfField(mutable = true, masterOnly = true, description = {
+            "启用外表DDL",
+            "Enable external table DDL"})
+    public static boolean enable_external_ddl = false;
+
+
     @ConfField(mutable = true, masterOnly = true, description = {
             "Hive创建外部表默认指定的input format",
             "Default hive input format for creating table."})