AppFlowy with Cloud build

For using [AppFlowy Cloud - Architecture - AppFlowy Docs](https://docs.appflowy.io/docs/documentation/appflowy-cloud/architecture), we need to pass [Step 4: Configure the AppFlowy Application - Self-hosting AppFlowy for free Using Supabase - AppFlowy Docs](https://docs.appflowy.io/docs/guides/appflowy/self-hosting-appflowy-using-supabase#step-4-configure-the-appflowy-application), which involves a Cloud Settings screen:


There is an example repository `AppFlowy-IO/AppFlowy-with-AppFlowy-Cloud-Build`, which has seen its first release yesterday.

* [AppFlowy-IO/AppFlowy-with-AppFlowy-Cloud-Build](https://github.com/AppFlowy-IO/AppFlowy-with-AppFlowy-Cloud-Build)
* [Releases · AppFlowy-IO/AppFlowy-with-AppFlowy-Cloud-Build](https://github.com/AppFlowy-IO/AppFlowy-with-AppFlowy-Cloud-Build/releases)
* [Current Limiations - Self-hosting AppFlowy with AppFlowy Cloud - AppFlowy Docs](https://docs.appflowy.io/docs/guides/appflowy/self-hosting-appflowy#current-limitations)

Maybe this will be interesting to replicate in FlatPak, eventually in a separate repository under a different name? Maybe the example is close enough to what is here already, and only minimal adaptations are needed.

Start by comparing the AppFlowy-IO/AppFlowy-with-AppFlowy-Cloud-Build repository and its first release with this Flatpak project, then read the linked AppFlowy Cloud architecture and self-hosting configuration documentation. Done means the required Cloud Settings configuration can be supported in the Flatpak build, with any remaining limitations documented.

Written by the indexing model from the issue text.