[improvement](mysql)Support mysql COM_RESET_CONNECTION command. (#44747)

### What problem does this PR solve?
Support mysql COM_RESET_CONNECTION command.
Doris server side reset default catalog and return
ctx.getState().setOk()

Python test code:
```
import mysql.connector

connection = mysql.connector.connect(
    host="172.20.32.136", 
    port=29030,
    user="root", 
    password="", 
    database=""
)
print(connection.cmd_reset_connection())
```

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

### Release note

None

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

@@ -342,6 +342,11 @@ public String removeLastDBOfCatalog(String catalog) {
         return lastDBOfCatalog.get(catalog);
     }
 
+    // Used by COM_RESET_CONNECTION
+    public void clearLastDBOfCatalog() {
+        lastDBOfCatalog.clear();
+    }
+
     public void setNotEvalNondeterministicFunction(boolean notEvalNondeterministicFunction) {
         this.notEvalNondeterministicFunction = notEvalNondeterministicFunction;
     }

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

@@ -44,6 +44,7 @@
 import org.apache.doris.common.util.SqlUtils;
 import org.apache.doris.common.util.Util;
 import org.apache.doris.datasource.CatalogIf;
+import org.apache.doris.datasource.InternalCatalog;
 import org.apache.doris.metric.MetricRepo;
 import org.apache.doris.mysql.MysqlChannel;
 import org.apache.doris.mysql.MysqlPacket;
@@ -198,6 +199,12 @@ protected void handleDebug() {
         ctx.getState().setOk();
     }
 
+    protected void handleResetConnection() {
+        ctx.changeDefaultCatalog(InternalCatalog.INTERNAL_CATALOG_NAME);
+        ctx.clearLastDBOfCatalog();
+        ctx.getState().setOk();
+    }
+
     protected void handleStmtReset() {
         ctx.getState().setOk();
     }

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

@@ -264,6 +264,9 @@ private void dispatch() throws IOException {
             case COM_SET_OPTION:
                 handleSetOption();
                 break;
+            case COM_RESET_CONNECTION:
+                handleResetConnection();
+                break;
             default:
                 ctx.getState().setError(ErrorCode.ERR_UNKNOWN_COM_ERROR, "Unsupported command(" + command + ")");
                 LOG.warn("Unsupported command(" + command + ")");