docs: add English version of upgrade

docs/en/maintain/index.rst

@@ -4,6 +4,5 @@ Maintenance
 
 .. toctree::
     :maxdepth: 1
-
     cli
-
+    upgrade

docs/en/maintain/upgrade.md

@@ -0,0 +1,58 @@
+# Upgrade
+
+Here is the impact when upgrading OpenMLDB:
+* If the created table is a single copy, it is not readable and writable during the upgrade process
+* If the created table is multi-replica, the read request on the upgraded node will fail briefly, and the write request will have a small amount of data loss.If short read failures are not tolerated, execute offlineendpoint before stopping each tablet node. If a small amount of write loss cannot be tolerated, write operations need to be stopped during the upgrade process
+
+## 1. Upgrade nameserver
+
+* Stop nameserver
+    ```bash
+    sh bin/start.sh stop nameserver
+    ```
+* Backup the old versions directories `bin` and `conf`
+* Download new version bin and conf
+* Compare the configuration file diff and modify the necessary configuration, such as endpoint, zk_cluster, etc
+* Start nameserver
+    ```bash
+    sh bin/start.sh start nameserver
+    ```
+* Repeat the above steps for the remaining nameservers
+
+## 2. Upgrade tablet
+
+* Stop tablet
+    ```bash
+        sh bin/start.sh stop tablet
+    ```
+* Backup the old versions directories `bin` and `conf`
+* Download new version bin and conf
+* Compare the configuration file diff and modify the necessary configuration, such as endpoint, zk_cluster, etc
+* Start nameserver
+    ```bash
+    sh bin/start.sh start tablet
+    ```
+* If auto_failover is closed, you must connect to the ns client and perform the following operations to restore data. **The endpoint after the command is the endpoint of the restarted node**
+  * offlineendpoint endpoint 
+  * recoverendpoint endpoint
+
+```
+$ ./bin/openmldb --zk_cluster=172.27.128.31:8090,172.27.128.32:8090,172.27.128.33:8090 --zk_root_path=/openmldb_cluster --role=ns_client
+> offlineendpoint 172.27.128.32:8541
+offline endpoint ok
+> recoverendpoint 172.27.128.32:8541
+recover endpoint ok
+```
+
+### Confirmation of Upgrade Result
+* showopstatus command checks whether all operations are kDone, and if there is a kFailed task, check the log to troubleshoot the cause
+* showtable to see if the status of all partitions is yes
+
+After a tablet node is upgraded, repeat the above steps for other tablets. \(**You must wait until the data is synchronized before upgrading the next node**\)
+
+After all nodes are upgraded, resume write operations, and run the showtable command to check whether the master-slave offset has increased
+
+## 3. Upgrade Java Client
+
+* Update the java client version number in the pom file
+* Update dependencies