Setting default backgrounds, and other settings && settings lockdown

[gdevenyi]

I discovered how to do this.

1. Create /etc/dconf/profile/user

user-db:user
system-db:site

2. Create site DB directory /etc/dconf/db/site.d/00-site

[x/dm/slick-greeter]
background='/usr/share/backgrounds/ubuntucinnamon/noble/Suamgol_Village_by_Joshua_Park.jpg'

[org/cinnamon/desktop/background]
picture-uri='file:///usr/share/backgrounds/ubuntucinnamon/noble/Suamgol_Village_by_Joshua_Park.jpg'

This can be a huge number of different configs, see dconf-editor

3. Create a locks directory/file, any keys listed here cannot be changed by the user /etc/dconf/db/site.d/locks/00-site

org/cinnamon/desktop/background/picture-uri

4. Run dconf-update

Ref:
https://wiki.gnome.org/Projects(2f)dconf(2f)SystemAdministrators.html
https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/desktop_migration_and_administration_guide/custom-default-values-system-settings#custom-default-values-system-settings