First, thanks for providing packages for Debian systems.

Unfortunately packages provided for zabbix-agent2 and its plugins have dependencies setup in a way that installing agent forcefully pull MongoDB and PostgreSQL plugins into the system.

Because of that setup those plugins would be installed on all systems where agent2 is installed even if they are not needed. That can not be overridden by system administrator by any means other than by providing fake packages for those plugins to fulfill agent unneeded dependencies.

Zabbix agent2 package should not depend on its plugins but plugins packages should depend on the agent2 package in some way.

Debian provides few levels of dependency between packages. As plugins do not strictly require agent (they are not linked to it and could be executed in its absence) but are practically nonfunctional without it, they should at least require it. In typical configuration that would pull in agent2 when one of the plugins is installed. In case of required (and not strict depend) system administrator would be able to still not install agent2 if that for some reason would be desired (but I myself do not know of any reason for that).

Agent package should not depend on its plugins nor require them but instead should suggest them or not depend on them at all. Suggesting them would strengthen discoverability but on typical system would not automatically make pulling plugins in.

As an alternative, instead of agent suggesting plugins, plugins may declare that they enhance agent.

The same should be done also for MS-SQL plugin package. Currently it do not depend on agent nor agent on it in any way.

Thorough explanation of dependency system in Debian can be found on its official documentation page https://www.debian.org/doc/debian-policy/ch-relationships.html

Regards