branch-3.1: [opt](compatibility) let version mutable apache#55335 (apache#56630)

picked from apache#55335

Author: morrySnow

fe/fe-core/src/main/java/org/apache/doris/mysql/MysqlHandshakePacket.java

@@ -17,6 +17,8 @@
 
 package org.apache.doris.mysql;
 
+import org.apache.doris.qe.GlobalVariable;
+
 // MySQL protocol handshake packet.
 public class MysqlHandshakePacket extends MysqlPacket {
     private static final int SCRAMBLE_LENGTH = 20;
@@ -25,7 +27,7 @@ public class MysqlHandshakePacket extends MysqlPacket {
     // JDBC uses this version to check which protocol the server support
     // Set the patch version to 99 to prevent the vulnerability scanning tool from
     // falsely reporting MySQL vulnerabilities
-    public static final String SERVER_VERSION = "5.7.99";
+    public static final String DEFAULT_SERVER_VERSION = "5.7.99";
     // 33 stands for UTF-8 character set
     private static final int CHARACTER_SET = 33;
     // use default capability for all
@@ -53,7 +55,7 @@ public void writeTo(MysqlSerializer serializer) {
         MysqlCapability capability = MysqlProto.SERVER_USE_SSL ? SSL_CAPABILITY : CAPABILITY;
 
         serializer.writeInt1(PROTOCOL_VERSION);
-        serializer.writeNulTerminateString(SERVER_VERSION);
+        serializer.writeNulTerminateString(GlobalVariable.version);
         serializer.writeInt4(connectionId);
         // first 8 bytes of auth plugin data
         serializer.writeBytes(authPluginData, 0, 8);

fe/fe-core/src/main/java/org/apache/doris/qe/GlobalVariable.java

@@ -87,8 +87,8 @@ public final class GlobalVariable {
             + Version.DORIS_BUILD_VERSION + "-" + Version.DORIS_BUILD_SHORT_HASH
             + (Config.isCloudMode() ? " (Cloud Mode)" : "");
 
-    @VariableMgr.VarAttr(name = VERSION, flag = VariableMgr.READ_ONLY)
-    public static String version = MysqlHandshakePacket.SERVER_VERSION;
+    @VariableMgr.VarAttr(name = VERSION)
+    public static String version = MysqlHandshakePacket.DEFAULT_SERVER_VERSION;
 
     // 0: table names are stored as specified and comparisons are case sensitive.
     // 1: table names are stored in lowercase on disk and comparisons are not case sensitive.