Adds configuration for the systemd-modules-load service, which loads kernel modules at boot based on configuration in /etc/modules-load.d/.

• DIB_SYSTEMD_MODULES_LOAD_FILE is the name of the file that will be added in /etc/modules-load.d/. The default value is dib.conf.
• DIB_SYSTEMD_MODULES_LOAD_CONTENT is the content to write to DIB_SYSTEMD_MODULES_LOAD_FILE. This variable is required.