/usr/share/ubuntu-defaults-builder/template/i18n/keyboard.txt is in ubuntu-defaults-builder 0.30.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | # Default keyboard layout for installer images built with this defaults
# package. Note that the defaults package itself does not configure the
# layout, this only gets effective for image builds.
#
# Format: single line with
# layout
# or
# layout variant
#
# Check /usr/share/X11/xkb/rules/xorg.lst for the complete list of available
# layouts and variants.
#
# Example:
# de nodeadkeys
|