[improvement](config)update FE config max_running_txn_num_per_db default value (#20478)

image update FE config max_running_txn_num_per_db default value: old value : 100 new value : 1000

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

@@ -562,7 +562,7 @@ public class Config extends ConfigBase {
             "单个数据库最大并发运行的事务数，包括 prepare 和 commit 事务。",
             "Maximum concurrent running txn num including prepare, commit txns under a single db.",
             "Txn manager will reject coming txns."})
-    public static int max_running_txn_num_per_db = 100;
+    public static int max_running_txn_num_per_db = 1000;
 
     @ConfField(masterOnly = true, description = {"pending load task 执行线程数。这个配置可以限制当前等待的导入作业数。"
             + "并且应小于 `max_running_txn_num_per_db`。",