Encrypted DB connection support for Agent2

Zabbix can natively encrypt DB connections using certificates since version 5.0

This is supported for both backend and frontend with different levels of security and works as expected.

Zabbix agent 2 has native plugins for MySQL and PostgreSQL monitoring, however these plugins do not support encrypted connections. This means that it is possible to enforce communication encryption on database level and have fully working Zabbix instance, but monitoring of databases will be no longer supported.

Expected: Zabbix agent2 plugins support encrypted database connections.