chore(default-flatpaks): Investigate if system-flatpak-setup needs to use `dbus-run-session`

[fiftydinar]

Some Universal Blue users are affected with the issue where they don't get any system flatpak updates when using built-in auto-update service from ublue-os/config (not to be confused with ublue-update): https://github.com/ublue-os/config/issues/168

Upstream issue: https://github.com/flatpak/flatpak/issues/3847

Fedora Silverblue & Kinoite are known as affected.

I personally never had a problem with both ublue-os/config flatpak auto-updates & default-flatpaks module.

But in order to avoid potential upstream issue, workaround would be to use dbus-run-session before executing flatpak binary.