Move hooks and install scripts from systemd to mkinitcpio

Probably needs more work

Command to reproduce this work:

pkgctl repo clone systemd
git-filter-repo --path initcpio-hook-udev --path initcpio-install-systemd --path initcpio-install-udev
git filter-repo \
  --path-rename initcpio-hook-udev:hook/udev \
  --path-rename initcpio-install-systemd:install/systemd \
  --path-rename initcpio-install-udev:install/udev
cd ../mkinitcpio
git checkout -b systemd-hooks
git remote add -f systemd ../systemd
git fetch --all
git merge systemd/main --allow-unrelated-histories

Note for any branch updates you can just cherry-pick changes.