Appcenter as a flatpak

### Problem

The hype around Bazaar has shown there is interest toward alternative options for flatpak app stores.
Bazaar is easy to install: It is on flathub. Two clicks and it is usable.

Appcenter is amazing but cannot be installed from the elementary remote. It is still a deb thing (which makes sense for a system app)
Maybe being able to try out Appcenter could motivate people from other distros to add the elementary flatpak remote? The news alone can bring some attention.
Appcenter also offers the unique feature to donate. This may encourage people to also add their app if appcenter became somewhat popular, and make it the "option if people want payment"

### Proposal

Offer Appcenter packaged as a flatpak on the remote

Im not sure how difficult that would be. Bazaar seems a bit messily built.

### Prior Art (Optional)

_No response_