Fix memory leak reported by valgrind in 'Query_Processor::new_query_rule'

[JavierJF]

• A clear description of the issue

Valgrind reports several bytes as definitely lost due to non-freeing of 'Query_Processor' field:

==667751== 28 bytes in 2 blocks are definitely lost in loss record 996 of 2,406
==667751==    at 0x483A77F: malloc (vg_replace_malloc.c:307)
==667751==    by 0x4E8DB4E: strdup (in /usr/lib/libc-2.32.so)
==667751==    by 0x47D826: Query_Processor::new_query_rule(int, bool, char*, char*, int, char*, char*, int, char*, char*, char*, bool, char*, int, char*, int, int, int, int, int, int, int, int, int, int, int, char*, char*, int, int, int, int, bool, char*) (Query_Processor.cpp:614)
==667751==    by 0x4DC23F: ProxySQL_Admin::load_mysql_query_rules_to_runtime() (ProxySQL_Admin.cpp:10331)
==667751==    by 0x4CC779: ProxySQL_Admin::init_mysql_query_rules() (ProxySQL_Admin.cpp:8863)
==667751==    by 0x3A593C: ProxySQL_Main_init_Query_module() (main.cpp:997)
==667751==    by 0x3A68B3: ProxySQL_Main_init_phase3___start_all() (main.cpp:1348)
==667751==    by 0x3A8146: main (main.cpp:1787)

• ProxySQL version

• v2.0.16

• v2.1.1 should also be affected.

• OS version

NAME="Arch Linux"
PRETTY_NAME="Arch Linux"
ID=arch
BUILD_ID=rolling

• The steps to reproduce the issue

Launch ProxySQL under and create new query rules.

• The full ProxySQL error log (default location: /var/lib/proxysql/proxysql.log)

valgrind.txt

[JavierJF]

Closed by #3264.