Do not change config files in post-install scripts anymore (with sed
commands or by other means). Instead, ship the files inside the packages
and use "replaces", so apk allows the package to overwrite files from
other packages:
https://wiki.alpinelinux.org/wiki/APKBUILD_Reference#replaces

Notes on specific files:
* /etc/elogind/logind.conf: original file only consists of commented out
  compile defaults. Copy them over for now. In the future we should be
  able to install our own config into a .d directory, without all the
  comments: https://github.com/elogind/elogind/commit/8358fc595027145bf1f3ff572a4c3f23b232830a
* /etc/fstab: original file only has /dev/cdrom and /dev/usbdisk
  entries, which are not useful for postmarketOS:
  https://gitlab.alpinelinux.org/alpine/aports/-/blob/master/main/alpine-baselayout/APKBUILD
* /etc/motd: reformat the text, add link to the chat
* /etc/conf.d/syslog: original file only contained 'SYSLOGD_OPTS="-t"',
  make the override file as if the sed statement from post-install was
  executed
* /etc/wpa_supplicant/wpa_supplicant.conf: post-install script touches
  this file. We probably added it back in 2017 in relation to enabling
  D-Bus (though the PR does not mention it explicity), but at least with
  the current init.d script of NetworkManager, we can simply have '-u' in
  wpa_supplicant_args:
  https://github.com/postmarketOS/pmbootstrap/pull/578
  https://gitlab.alpinelinux.org/alpine/aports/-/blob/master/main/wpa_supplicant/wpa_supplicant.initd
* /etc/sudoers: base on original /etc/sudoers, but remove all the
  commented out stuff except for the visudo note at the top. We could
  also put a file in /etc/sudoers.d, but since the wheel line is present
  in the original /etc/sudoers and only commented out, it would be kind
  of unexpected to enable it in a file in /etc/sudoers.d. I prefer this
  stripped down version of the file, that is easy to read.