experimental: v2023.2.5 for 2025_08_22

This update required bigger changes: moving information from "site.mk"
to a new file called "image-customization.lua".

I do not like the x86-specific packages, but I kept them as nobody told
me if they were needed or not.

Revert "Add new xbr signing keys // 2023.1.0 20240714"

This reverts commit 228ce089848887a8525d78e83798182ac128ffcb.
Signing keys were found.

Add scripts for automation of building and build machine setup

This allows us to use a powerful Hetzner VM for not very long to
build our firmware in almost no time.