Draft: community/gnome-software-plugin-apk: drop install_if on GS

Since there is the use-case of using GNOME Software exclusively for Flatpak, it could be convenient to split the APK plugin.

TODO

• Add to Alpine release notes
• Add the plugin to gnome metapackage
• Have https://gitlab.com/postmarketOS/postmarketos-release-upgrade/-/merge_requests/10 merged
• Add pmOS edge blog-post warning people to add it