[Config]Remove max_user_connections from config (apache#3805)

Update max_user_connections by user property:

```
set property `user` max_user_connections=100;
```

Author: EmmyMiao87

docs/.vuepress/sidebar/en.js

@@ -98,6 +98,7 @@ module.exports = [
         children: [
           "fe_config",
           "be_config",
+          "user_property,
         ],
         sidebarDepth: 1,
       },

docs/.vuepress/sidebar/zh-CN.js

@@ -107,6 +107,7 @@ module.exports = [
         children: [
           "fe_config",
           "be_config",
+          "user_property",
         ],
         sidebarDepth: 1,
       },

docs/en/administrator-guide/config/user_property.md

@@ -0,0 +1,69 @@
+--- 
+{
+    "title": "User Property",
+    "language": "en"
+}
+---
+
+<!-- 
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+# User configuration item
+
+This document mainly introduces related configuration items at the User level. The configuration of the User level is mainly effective for a single user. Each user can set their own User property. Does not affect each other.
+
+## View configuration items
+
+After the FE is started, on the MySQL client, use the following command to view the User configuration items:
+
+`SHOW PROPERTY [FOR user] [LIKE key pattern]`
+
+The specific syntax can be queried through the command: `help show property;`.
+
+## Set configuration items
+
+After FE is started, on the MySQL client, modify the User configuration items with the following command:
+
+`SET PROPERTY [FOR'user'] 'key' = 'value' [,'key' ='value']`
+
+The specific syntax can be queried through the command: `help set property;`.
+
+User-level configuration items will only take effect for the specified users, and will not affect the configuration of other users.
+
+## Application examples
+
+1. Modify the max_user_connections of user Billie
+
+    Use `SHOW PROPERTY FOR 'Billie' LIKE '%max_user_connections%';` to check that the current maximum number of links for Billie users is 100.
+
+    Use `SET PROPERTY FOR 'Billie' 'max_user_connections' = '200';` to modify the current maximum number of connections for Billie users to 200.
+
+## Configuration item list
+
+### max_user_connections
+
+    The maximum number of user connections, the default value is 100 In general, this parameter does not need to be changed unless the number of concurrent queries exceeds the default value.
+
+### resource
+
+### quota
+
+### default_load_cluster
+
+### load_cluster

docs/zh-CN/administrator-guide/config/fe_config.md

@@ -371,8 +371,6 @@ FE 的配置项有两种方式进行配置：
 
 ### `max_connection_scheduler_threads_num`
 
-### `max_conn_per_user`
-
 ### `max_create_table_timeout_second`
 
 ### `max_distribution_pruner_recursion_depth`

docs/zh-CN/administrator-guide/config/user_property.md

@@ -0,0 +1,69 @@
+---
+{
+    "title": "用户配置项",
+    "language": "zh-CN"
+}
+---
+
+<!-- 
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+# User 配置项
+
+该文档主要介绍了 User 级别的相关配置项。User 级别的配置生效范围为单个用户。每个用户都可以设置自己的 User property。相互不影响。
+
+## 查看配置项
+
+FE 启动后，在 MySQL 客户端，通过下面命令查看 User 的配置项：
+
+`SHOW PROPERTY [FOR user] [LIKE key pattern]`
+
+具体语法可通过命令：`help show property;` 查询。
+
+## 设置配置项
+
+FE 启动后，在MySQL 客户端，通过下面命令修改 User 的配置项：
+
+`SET PROPERTY [FOR 'user'] 'key' = 'value' [, 'key' = 'value']`
+
+具体语法可通过命令：`help set property;` 查询。
+
+User 级别的配置项只会对指定用户生效，并不会影响其他用户的配置。
+
+## 应用举例
+
+1. 修改用户 Billie 的 `max_user_connections`
+
+    通过 `SHOW PROPERTY FOR 'Billie' LIKE '%max_user_connections%';` 查看 Billie 用户当前的最大链接数为 100。
+
+    通过 `SET PROPERTY FOR 'Billie' 'max_user_connections' = '200';` 修改 Billie 用户的当前最大连接数到 200。
+
+## 配置项列表
+
+### max_user_connections
+
+    用户最大的连接数，默认值为100。一般情况不需要更改该参数，除非查询的并发数超过了默认值。
+
+### resource
+
+### quota
+
+### default_load_cluster
+
+### load_cluster

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

@@ -668,10 +668,6 @@ public class Config extends ConfigBase {
      * Maximal number of connections per FE.
      */
     @ConfField public static int qe_max_connection = 1024;
-    /*
-     * Maximal number of connections per user, per FE.
-     */
-    @ConfField public static int max_conn_per_user = 100;
 
     /*
      * Maximal number of thread in connection-scheduler-pool.

fe/src/main/java/org/apache/doris/mysql/privilege/UserProperty.java

@@ -74,7 +74,7 @@ public class UserProperty implements Writable {
 
     private String qualifiedUser;
 
-    private long maxConn = Config.max_conn_per_user;
+    private long maxConn = 100;
     // Resource belong to this user.
     private UserResource resource = new UserResource(1000);
     // load cluster