gnome-software should (?) be separated from the packagekit

Given that the Snap Store is currently the default in Ubuntu instead of GNOME Software, the only reason GNOME Software (along with the Snap Store) can be installed is to support Flatpak applications.

In the current instance, if you want to add flatpak support, GNOME Software is installed with both the apt packagekit add-on and the flatpak plugin, which is duplication of work (Software Updater already works on updates, and Snap Store works on showing deb apps).

And since the future app store explicitly refuses [1], [2] to support flatpak applications, users who need this package format will be forced to put GNOME Software with everything I pointed out above.

Therefore, it would be very nice if the developers removed the packagekit add-on from the "gnome-software part" and made it a "plug-in for gnome-software".

I, unfortunately, have no such experience with packaging deb packages at the moment, and it turns out that it will obviously be necessary to work out both the code part (which, as far as I can see, won't be very difficult [3]), as well as the part where we will have to figure out where and how to insert the plugin as mandatory (for example, when the user completely gives up on snap packages) and as optional (because the Snap Store already stands).

Also, let me know if this needs to be sent to upstream (Debian) instead of here.
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1. https://github.com/ubuntu-flutter-community/software/issues/126
2. https://github.com/ubuntu-flutter-community/software/issues/30
3. https://build.opensuse.org/request/show/1031279