[opt](variables) enlarge the default value of max_allowed_packet (apa…

…che#38697)

From 1MB to 16MB, same as MySQL 8.4.
This is to avoid "Packet for query is too large" error
when querying wide table or table with wide column.

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

@@ -813,7 +813,7 @@ public class SessionVariable implements Serializable, Writable {
 
     // this is used to make c3p0 library happy
     @VariableMgr.VarAttr(name = MAX_ALLOWED_PACKET)
-    public int maxAllowedPacket = 1048576;
+    public int maxAllowedPacket = 16777216;
 
     @VariableMgr.VarAttr(name = AUTO_INCREMENT_INCREMENT)
     public int autoIncrementIncrement = 1;