I created a flatpak configuration file for a release on Flathub.

• Set up the mime type and application icon
• Check if the sandboxing is set up correctly
• Revisit the mime-types in the snap configuration so both can be synced
• Add gradle tasks for local builds/installs
• Create an automation that will dynamically generate the flat hub file and create a PR on the target repo

To consider:

• Should we add a single file to the releases so people can install the flatpak version without flathub?

Closes #890