Consider migrating some of /lib/live/config/* to systemd unit files

While working on reproducible builds we’re adding quite some stuff in there, and some of it might be slow. If this affects boot time significantly (especially on slower hardware), we should migrate some of those bits to systemd unit files, so that they can be run in parallel.

Feature Branch: bugfix/11971-fontconfig-cache-in-iso

Parent Task: #5630 (closed)

Related issues

Related to #12318
Related to #11983 (closed)
Related to #12567 (closed)

Original created by @intrigeri on 11971 (Redmine)

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