Agent2: restrict available checks on the agent side

As a security measure, Zabbix agent provides a configuration parameter EnableRemoteCommands to restrict system.run[] checks.

However, system.run[] is not the only way to compromise security through Zabbix agent. For instance, a malicious administrator can potentially query vfs.file.contents[] on a user's workstation to peek on files in the system that contain cached passwords.

Thus, it would be nice if there would be a way to restrict availability of arbitrary checks on the agent, not just system.run[].

C agent implementation done in parent task: ZBXNEXT-1085

ACC: https://confluence.zabbix.lan/x/Q5RLAw
SPEC: https://confluence.zabbix.lan/x/xJZLAw
PLAN: https://teamplan.zabbix.lan/project/view/3431