feat: add flatpak-preinstalld service and apps proposition

[jumpyvi]

Draft based on zirconium

fixes #6

Includes:

• Web (As a temporary browser on new install, having no browser at all is super annoying)
• TextEditor (Pretty much everyone needs one)
• Bazaar (It's cool)
• Firmware (We remove gnome-software)
• ExtensionManager (No one uses vanilla gnome)
• FileRoller (Archive)
• Loupe (Basic utils)
• Papers (Basic utils)
• Refine (Not sure if it's needed, it doesnt do much, it would be better to ship gnome-tweaks from gnome's flatpak repo)

[fizzyizzy05]

I think I might add to this at some point, just so we have a more complete set of default apps, but this is a good starting point. I might do that later.

[fizzyizzy05]

Mentioned this on Discord already, but Firefox is probably a better default than Epiphany IMHO, since it has better support for things like extensions and cross-device sync

[fizzyizzy05]

Not against this, though I think it'd be better to just promote this in Bazaar instead under the curated section.

[fizzyizzy05]

See also: #52

[fizzyizzy05]

Same as Extension Manager

[fizzyizzy05]

LGTM

[fizzyizzy05]

Rebased this on main. I've enabled it by default (for now) so it should work out of the box.

I'm thinking that this should be treated as a source of truth for preinstalled applications, users wanting to reinstall the bundled apps can run flatpak preinstall and whatever we use to build the ISO can do the same thing before copying the /var/lib/flatpak folder over to the new install.

That also probably means we should probably add most of the GNOME core apps here, as well as Resources for a system monitor replacement, so it's more complete.