/usr/share/icinga2/include/plugins-contrib.d/ is in icinga2-common 2.8.1-0ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/icinga2/include/plugins-contrib.d/databases.conf
/usr/share/icinga2/include/plugins-contrib.d/hardware.conf
/usr/share/icinga2/include/plugins-contrib.d/icingacli.conf
/usr/share/icinga2/include/plugins-contrib.d/ipmi.conf
/usr/share/icinga2/include/plugins-contrib.d/logmanagement.conf
/usr/share/icinga2/include/plugins-contrib.d/metrics.conf
/usr/share/icinga2/include/plugins-contrib.d/network-components.conf
/usr/share/icinga2/include/plugins-contrib.d/network-services.conf
/usr/share/icinga2/include/plugins-contrib.d/operating-system.conf
/usr/share/icinga2/include/plugins-contrib.d/raid-controller.conf
/usr/share/icinga2/include/plugins-contrib.d/smart-attributes.conf
/usr/share/icinga2/include/plugins-contrib.d/storage.conf
/usr/share/icinga2/include/plugins-contrib.d/virtualization.conf
/usr/share/icinga2/include/plugins-contrib.d/vmware.conf
/usr/share/icinga2/include/plugins-contrib.d/web.conf