[improvement](catalog) Change the push-down parameters of the predicate function of the table query SQL into variables (#30028)

In this PR, we will control whether the external data source query is a push-down function parameter in the filter condition, changing the enable_fun_pushdown of fe conf to the enable_ext_func_pred_pushdown of the variable

fe/fe-common/src/main/java/org/apache/doris/common/Config.java

@@ -1921,13 +1921,6 @@ public class Config extends ConfigBase {
     @ConfField(mutable = false, varType = VariableAnnotation.EXPERIMENTAL)
     public static boolean enable_fqdn_mode = false;
 
-    /**
-     * This is used whether to push down function to MYSQL in external Table with query sql
-     * like odbc, jdbc for mysql table
-     */
-    @ConfField(mutable = true)
-    public static boolean enable_func_pushdown = true;
-
     /**
      * If set to true, doris will try to parse the ddl of a hive view and try to execute the query
      * otherwise it will throw an AnalysisException.