/etc/freeradius/3.0/huntgroups is in freeradius-config 3.0.16+dfsg-1ubuntu3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /etc/freeradius/3.0/mods-config/preprocess/huntgroups
/etc/freeradius/3.0/mods-config/preprocess/huntgroups