[fix](jdbc catalog) set enable_jdbc_cast_predicate_push_down defaul…

…t true (#44548)

### What problem does this PR solve?

Related PR: #42102

Problem Summary:

We found that after disabling pushdown of predicates with implicit
casts, some users experienced slower queries, so we temporarily changed
this parameter back to the default behavior.

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

@@ -686,7 +686,7 @@ public class SessionVariable implements Serializable, Writable {
     @VariableMgr.VarAttr(name = ENABLE_JDBC_CAST_PREDICATE_PUSH_DOWN, needForward = true,
             description = {"是否允许将带有 CAST 表达式的谓词下推到 JDBC 外部表。",
                     "Whether to allow predicates with CAST expressions to be pushed down to JDBC external tables."})
-    public boolean enableJdbcCastPredicatePushDown = false;
+    public boolean enableJdbcCastPredicatePushDown = true;
 
     @VariableMgr.VarAttr(name = ROUND_PRECISE_DECIMALV2_VALUE)
     public boolean roundPreciseDecimalV2Value = false;

regression-test/suites/external_table_p0/jdbc/test_clickhouse_jdbc_catalog.groovy

@@ -82,17 +82,11 @@ suite("test_clickhouse_jdbc_catalog", "p0,external,clickhouse,external_docker,ex
             sql("select * from ts where from_unixtime(ts,'yyyyMMdd') >= '2022-01-01';")
             contains """QUERY: SELECT "id", "ts" FROM "doris_test"."ts" WHERE ((FROM_UNIXTIME("ts", '%Y%m%d') >= '2022-01-01'))"""
         }
-        explain {
-            sql("select * from ts where nvl(ts,null) >= '1';")
-            contains """QUERY: SELECT "id", "ts" FROM "doris_test"."ts"""
-        }
         order_qt_func_push2 """select * from ts where ts <= unix_timestamp(from_unixtime(ts,'yyyyMMdd'));"""
-        sql "set enable_jdbc_cast_predicate_push_down = true;"
         explain {
             sql("select * from ts where ts <= unix_timestamp(from_unixtime(ts,'yyyy-MM-dd'));")
             contains """QUERY: SELECT "id", "ts" FROM "doris_test"."ts" WHERE (("ts" <= toUnixTimestamp(FROM_UNIXTIME("ts", '%Y-%m-%d'))))"""
         }
-        sql "set enable_jdbc_cast_predicate_push_down = false;"
 
         order_qt_dt_with_tz """ select * from dt_with_tz order by id; """
 

regression-test/suites/external_table_p0/jdbc/test_jdbc_catalog_push_cast.groovy

@@ -34,6 +34,8 @@ suite("test_jdbc_catalog_push_cast", "p0,external,mysql,external_docker,external
             "driver_class" = "com.mysql.cj.jdbc.Driver"
         );"""
 
+        sql "set enable_jdbc_cast_predicate_push_down = false;"
+
         sql "use jdbc_catalog_push_cast.doris_test"
 
         qt_sql """select * from test_cast where date(datetime_c) = '2022-01-01';"""