main/postmarketos-base: split apk-tools into -apk subpkg

It doesn't make sense to install apk by default in all flavors of pmOS,
like duranium. To avoid this, apk-tools is moved into a new -apk
subpackage that is pulled in implicitly via install_if. This has the
following benefits:

- postmarketos-duranium can "depend" on !postmarketos-base-apk to
exclude apk-tools

- apk-tools remains a dependency in existing mutable pmOS installs,
so it shouldn't be purged by this change 🤞

- we don't have to update hundreds of APKBUILDs in pmaports that
explicitly depend on `postmarketos-base` to now depend on some other
package that doesn't have apk-tools as an explicit dependency.

After this change, we'll be able to remove some janky cleanup code in
the duranium image build config for uninstalling apk-tools from the base
image, and it will allow us to *add* apk-tools in a system extension
later [1]

Signed-off-by: Clayton Craft <craftyguy@postmarketos.org>

1. https://gitlab.postmarketos.org/postmarketOS/pmaports/-/work_items/4502

Part-of: <https://gitlab.postmarketos.org/postmarketOS/pmaports/-/merge_requests/8426>

main/postmarketos-base/APKBUILD

@@ -1,7 +1,7 @@
 # Co-Maintainer: Achill Gilgenast <achill@achill.org>
 maintainer="Clayton Craft <clayton@craftyguy.net>"
 pkgname=postmarketos-base
-pkgver=57
+pkgver=58
 pkgrel=0
 pkgdesc="Meta package for minimal postmarketOS base"
 url="https://postmarketos.org"
@@ -12,7 +12,6 @@ makedepends="postmarketos-initramfs"
 # recommendation to not depend on openrc has been to copy them here:
 # https: // gitlab.alpinelinux.org/alpine/aports/-/merge_requests/71686#note_435428
 depends="
-	apk-tools
 	busybox
 	devicepkg-utils>=0.2.0
 	eudev
@@ -31,6 +30,7 @@ _pmb_recommends="sudo-rs"
 install="$pkgname.post-install $pkgname.post-upgrade"
 triggers="$pkgname.trigger=/usr/share/deviceinfo"
 subpackages="
+	$pkgname-apk:_apk
 	$pkgname-core
 	$pkgname-doas
 	$pkgname-fwupd
@@ -133,6 +133,17 @@ package() {
 	done
 }
 
+_apk() {
+	pkgdesc="apk-tools for mutable postmarketOS installations"
+	# The apk-tools dependency is in a subpackage so that other packages are able to
+	# depend on postmarketos-base AND exclude apk-tools at the same time with
+	# !postmarketos-base-apk
+	install_if="$pkgname=$pkgver-r$pkgrel"
+	depends="apk-tools"
+
+	mkdir -p "$subpkgdir"
+}
+
 core() {
 	# This is needed for backwards compatibility with installs that got
 	# the alpine-baselayout-core package in world: