If using Zabbix operator for Openshift (Version 5.0) and lets say there's one container with the agent per node, it would be very useful to know which container is running on which node.

Other operators pass a NODE_NAME environment variable to the container with the fieldRef spec.nodename. For example, in the screenshot is the configuration as Red Hat configured the cluster-logging operator/ how the ClusterLogging Operator configures the Daemonset. With this configuration access to the node name is possible within each pod using the environment variable.
If this were to be implemented, this it might be an idea to set the zabbix configuration so that the hostsname is set using Env[‘Node_NODE’] - so that the host in Zabbix would have the name of the node and not of the pod which is much more meaningful.
Since the deamon set is managed by the zabbix operatior every change is overwritten with each update of the operator.