/etc/cobbler/pxe/grubprofile.template is in maas-provision-common 2.2.2-0ubuntu4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 | title $profile_name
    root (nd)
    kernel $kernel_path $kernel_options
    initrd $initrd_path
 |