systemd/postmarketos-base-systemd: add zram-init/zram_swap preset (MR 6208)

I evaluated using systemd/zram-generator but decided against it for the following reasons:

1) it was more difficult to configure using the existing deviceinfo var
we have for zram_pct, this meant that we would ultimately couldn't have
a consistent way to configure zram stuff for all supported init systems

2) it's a Rust app, and was failing to build in CI for armv7, riscv64,
and armhf with some weird qemu crashes, failed tests, etc

3) zram-init Just Works, upstream ships a unit file for it so they
support running under systemd already
[ci:skip-build]: already built successfully in CI

extra-repos/systemd/postmarketos-base-systemd/APKBUILD

@@ -2,7 +2,7 @@
 # Co-maintainer: Clayton Craft <clayton@craftyguy.net>
 # pmbootstrap installs this, if systemd is selected in "pmbootstrap init".
 pkgname=postmarketos-base-systemd
-pkgver=26
+pkgver=27
 pkgrel=0
 pkgdesc="Meta package for running postmarketOS with systemd"
 url="https://postmarketos.org"
@@ -73,7 +73,7 @@ sha512sums="
 fbaa33425e507062a454f11bda48508f261c2144e5c23a20f567dc1cef14ce1dec57f8d934f418f5b6095509757f8503481aba9790a04c8f9f6995e65833d8c9  rootfs-etc-profile.d-99motd.sh
 2faac294bb632762e247b850f09ff4b544ccff6c462efd8d4faca71ba30bdfa9c460377a0dc88e92c5dbbe251017d164064a56ac0e0410f224b45d4f5f81866c  rootfs-etc-systemd-logind.conf
 15423bfda57c90ab62fe69865ca4072a0aeb83bf77d9c278257e346f4da81843d010b41003c91ae9f3fcb1c67447645e7c19078eea2bf11312051e6ad7523ad1  rootfs-usr-share-mkinitfs-files-extra-01-initramfs-base-systemd.files
-fb69154ca6f55e49992f38c9c1b34dba6f08fcbf36dcb85e21519879c58b47c833babbc1c55e160a414c347d4f546cec477565368995fbab6632a23156637df4  rootfs-usr-lib-systemd-system-preset-90-base.preset
+0e30cad5ab3a84807c406b66e391bf4c420d40c763fdb768a8194a499b91a705c18233921ad62d2d201de3fe3386e970cfddf55c38b6ba42fd565322ab51fe5e  rootfs-usr-lib-systemd-system-preset-90-base.preset
 c7ec5a4e7c7dcbf855f34e80adb225f52221340099216e57792b04f07e7b367e004209551e9a74152d9212926aba1b1a0a2680d3c2e35f15cca6f3cf0c9a3841  rootfs-usr-lib-systemd-user-preset-90-base.preset
 605df1f004783d2e0ec5dd99a688bca27502c8c24bc05fb4dc26589b2070b0fbd1cf9bd56e6861d7cda2f8ac8147e7eb040acfd886185c01c8cf9de8b1ce2dcd  rootfs-usr-bin-setup-timezone
 "

extra-repos/systemd/postmarketos-base-systemd/rootfs-usr-lib-systemd-system-preset-90-base.preset

@@ -26,6 +26,7 @@ enable systemd-rfkill.service
 enable tinydm.service
 enable udisks2.service
 enable cups.service
+enable zram_swap.service
 
 # Note: technically these two shouldn't be enabled at the same time, but
 # pmos-base-wifi provides should make sure that only one is installed at the