systemd/postmarketos-base-systemd: run systemctl on preset changes for already installed units

Closes: #3494 (closed)

Example output:

> sh postmarketos-base-systemd.post-install
unit policy has changed for systemd-journald-audit.socket
Failed to preset unit: Access denied
unit policy has changed for systemd-resolved*
  wildcards are not supported yet, skipping

How to test:

• Comment out the remove_old calls
• edit path to local file in check_and_apply_presets
• Comment out systemd_service_post_install call, probably replace it by an echo