Allow mgr module zabbix to run /usr/bin/zabbix_sender

The snap definition needs to be updated to allow the ceps mgr module for zabbix to be able to access the /usr/bin/zabbix_sender binary outside of the sandbox.

Locate the snap definition for the ceph mgr zabbix module and inspect how access to external binaries is declared. Verify the change specifically permits /usr/bin/zabbix_sender outside the sandbox, then test or validate the snap configuration for that access.

Written by the indexing model from the issue text.